Introduction: Chronic kidney disease (CKD) is recognized as global public health issue especially affecting developing countries including Thailand. The epidemiologic data in the decline of renal function and the risk factors among Thai patients especially in community hospital settings were limited. Methods: A cross-sectional study was conducted to identify the prevalence and associated risk factors in the decline of renal function among outpatients in Thaluang Community Hospital, Lop Buri Province, central Thailand, between November 1, 2018 and October 31, 2019. The decline in renal function was defined by glomerular filtration rate (GFR) <60 mL/min/1.73m2. Multivariate logistic regression analysis was performed to obtain the adjusted odds ratios (AOR) and 95% confidence interval (CI) of the factors related to the decline of renal function. Results: A total of 874 outpatients participated in the study. The overall prevalence in the decline of renal function (eGFR <60 mL/min/1.73m2) was 20.3% (95% CI; 17.5%-22.9%). Among male participants, the prevalence in the decline of renal function was 21.1% (95%CI; 16.7%-25.5%) while it totaled 19.7% (95%CI; 16.3%-23.1%) among females. The independent associated factors in the decline of renal function included greater age (AOR 1.07; 95% CI=1.05-1.09), history of NSAIDs used (AOR 2.97; 95% CI=1.85-4.79) and elevated pulse pressure (PP) >75th percentile (AOR 1.64; 95% CI=1.07-2.53) Conclusion: We reported the prevalence in the decline of renal function among outpatients in a Thai community hospital which was comparable with the national level. Advanced age, history of NSAIDs used and PP were related to reduced kidney function. Therefore, effective health interventions should be conducted especially, appropriate NSAIDs used among outpatients.