Based on 14 climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), uncertainty on the simulated summer precipitation over Eastern China is analyzed by investigating the intercomparison between individual model and multimodel ensemble (MME). Generally, MME has the ability in reproducing summer precipitation over Eastern China. However, large model spread exists among models in both climatology and interannual variation. The possible reason for the large model spread lies in the uncertainties on simulating large-scale circulations, e.g., East Asian subtropical westerly jet, western Pacific subtropical high, and East Asian summer monsoon. To investigate uncertainties in different regions, Eastern China is divided to four subregions: South China (SC), Yangtze-Huaihe River Basin (YHRB), North China (NC), and Northeast China (NEC). The annual cycle of regional mean precipitation from 14 CMIP5 models indicates that the model spread approaches maximum in early summer over SC and YHRB and in middle summer over NC and NEC. Uncertainties generally decrease from south to north, with the most sensitive region of SC. For different-class precipitation, the uncertainties of 14 models are small in relatively weak rain, but large in heavy and nonrainfall for all the four regions. We propose two possible reasons for the large uncertainties: different partitioning of stratiform/convective precipitation and horizontal resolutions.