Background Environmental characteristics are known to be associated with patterns of physical activity (PA). factor analysis. Reliability was assessed with test re-test reliability and internal consistency using Spearman r and Cronbach’s alpha respectively. Results Thirty six items were selected after the expert ratings and were developed into interviewer Fangchinoline administered questions. Exploration of factor structure of the 34 items which were factorable through principal component analysis with Quartimax rotation extracted 8 factors. The 34 item instrument was assessed for construct validity with confirmatory factor analysis which confirmed an 8 factor model (x2?=?339.9, Fangchinoline GFI?=?0.90). The identified factors were Fangchinoline infrastructure for walking, aesthetics and facilities for cycling, vehicular traffic safety, access and connectivity, recreational facilities for PA, safety, social cohesion and social acceptance of PA with the two non-factorable factors, residential density Fshr and land use mix. The PASES also showed good test re-test reliability and a moderate level of internal consistency. Conclusions The PASES is a valid and reliable tool which could be used to assess the physical and social environment associated with PA in Sri Lanka. Keywords: Physical and social environment, Physical activity, Development of a tool Background The burden of mortality, morbidity and disability due to non-communicable diseases (NCDs) is high and is increasing in the developing countries . Physical inactivity is identified as the fourth leading risk factor for mortality due to NCDs and contributes to 6% of deaths globally . In 2001, 71% of all deaths in Sri Lanka were due to chronic NCDs and chronic NCD mortality is reported to be 20-30% higher in Sri Lanka than in many developed countries . According to the Annual Health Statistics, coronary heart disease was the leading cause of hospital deaths in Sri Lanka since 1997 . The World Health Survey data collected in 2002C2003 revealed that in Sri Lanka 7.3% of the males and 13.8% of the females were physically inactive . Being physically active is influenced by both the physical and social environment [6, 7] and is best explained through a socio-ecological model of health related behaviours. Many studies have recognized that environmental factors have a significant role in promoting PA among adults [8-13] and changing behaviours in an entire community . Literature identifies some common physical (built) environment factors associated with PA. They are land-use patterns, transport systems, urban design, green space, availability of pavements, heavy traffic, street lights, unattended dogs, enjoyable scenery, high levels of crime, and easy access to recreation and retail shops [15,16]. Income, equity, culture and social support are identified in literature as elements in the social environment that influences participation in PA [17,18]. Considering the apparent importance of the environment for PA, there is limited information in the literature on how best to measure various aspects of the environment. Evidence on the associations between the physical environment and PA behaviour is derived mostly from self-reported data on individuals perceptions of their environments . Observational methods is another form where individuals using checklists, rates the environment. The introduction of geographic information systems into PA research has revolutionised the measurement of the physical environment, and is still in its early stages . Two major types of PA that have been studied in relation to the environment are the recreational PA and PA through non motorized transportation- walking/cycling. An accepted method of measuring the perceived physical environment is through population based studies and surveillance systems . Individual responses can then be aggregated to identify patterns in environment characteristics. Thereafter, it is possible to determine the association between the design characteristics of the environment and behaviour . There are different tools developed for assessment of environment characteristics that are related to different types of PA. Abbreviated Neighbourhood Environment Walkability Scale (ANEWS) and the International Physical Activity Questionnaire- environmental (IPAQ-e) are two tools.