The prosocial tendency of a city has become an important indicator to evaluate the urban social environment. Moreover, a series of small-sample studies have provided evidence of significant differences in the prosocial behavior of cities. These findings raise some questions: Does urbanization make people more indifferent? What are the differences in the prosocial tendencies of cities resulting from the urbanization process? Does economic development affect urban prosocial tendencies? These questions need to be urgently addressed in China, given its rapid urbanization and drastic social transformation. In this study, we constructed prosocial indexes for 95 Chinese cities based on Sina Microblog data for 2017, explored the laws governing the prosocial index of cities and examined the relationship between the urban economy and prosocial tendencies. Results showed significant differences between prosocial indexes at the region and tier level. At the region level, the highest prosocial index is in Northwest China and the lowest in East China. At the tier level, the highest index is in tier-5 cities, followed by tier-1 cities, while the lowest is in tier-3 cities. Further analysis indicated that urban GDP and prosocial tendencies have a u-shaped curvilinear correlation. Understanding the characteristics of prosocial tendencies could provide insights to enhance the quality of the urban social environment.