Little is known about how to effectively increase bystander cardiopulmonary resuscitation (CPR), so we evaluated the 10-year trend of the proportion of bystander CPR in an area with wide dissemination of chest compression-only CPR (CCCPR) training combined with conventional CPR training.Methods and Results: We conducted a descriptive study after a community intervention, using a prospective cohort from September 2010 to December 2019. The intervention consisted of disseminating CCCPR training combined with conventional CPR training in Toyonaka City since 2010. We analyzed all non-traumatic out-of-hospital cardiac arrest (OHCA) patients resuscitated by emergency medical service personnel. The primary outcome was the trend of the proportion of bystander CPR. We conducted multivariate logistic regression models and assessed the adjusted odds ratio (AOR) using a 95% confidence interval (CI) to determine bystander CPR trends. Since 2010, we have trained 168,053 inhabitants (41.9% of the total population of Toyonaka City). A total of 1,508 OHCA patients were included in the analysis. The proportion of bystander CPR did not change from 2010 (43.3%) to 2019 (40.0%; 1-year incremental AOR 1.02 [95% CI: 0.98-1.05]). The proportion of bystander CPR did not increase even after wider dissemination of CPR training. In addition to continuing wider dissemination of CPR training, other strategies such as the use of technology are necessary to increase bystander CPR.