With contemporary development of digital technology and smart cities initiatives, citizen co-production has created a new government-citizen interface. However, it remains inconclusive whether such citizen-government collaboration has achieved the fundamental goal of improving service quality for citizens. In this research, we tested the relationship between e-participation as a form of co-production and service performance, using multiple large longitudinal datasets from a smart city mobile platform. The results of the analysis show that citizen e-participation, in providing service feedback, is positively associated with the clearance rate of urban service requests in subdistrict service units, after controlling for various factors. We also found that the effect size of e-participation on service performance varies between different types of city services. E-participation has a stronger relative influence on complex problems that may involve multiple agencies, than with simple routine services.