OBJECTIVE : The interest in built environment attributes on physical activity has been rapidly increasing over recent decades. This study aimed to investigate the associations between residential density (RD) and walking time (WT), a common mode of physical activity, among urban adults in China. METHODS : This is a cross-sectional study. METHODS : Locally registered adults aged 35-74 years were randomly selected from eight urban neighbourhoods in Nanjing, China, in 2017. The outcome variable was self-reported WT (dichotomised), whereas RD (in tertiles) was the independent variable. Mixed-effects regression models were introduced to examine the RD-WT association via computing odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS : Of 1568 eligible participants, 98.9% completed the survey, with a mean age (standard deviation) of 54.7 (11.1) years, in which 46% were men. After adjustment for potential confounders, a negative gradient RD-WT association was seen across RD tertiles among the participants (OR = 2.88 [95% CI = 1.79, 4.64] and 2.10 [95% CI = 1.35, 3.26] for lower and middle tertiles, respectively, compared with the upper RD tertile). The negative RD-WT association was observed for both men and women. CONCLUSIONS : RD was negatively associated with the WT of urban adults in China. These results have public health implications for improving community-level physical activity through development of walking-friendly built environment.