As a prime biological role of longan, antioxidation is reported to be closely related to the richness of phenolic compounds. There is a large variation in total phenolics content and phenolic composition among different sub-cultivars of plants, yet the corresponding data as for longan pulps are still insufficient. For this reason, ten of Chinese longan cultivars were selected in this study for the determination of total phenolics and individual phenolic compounds. Four model assays were used to measure the antioxidant capacity of the extracts. Results showed that the free phenolics accounted for the major proportion in total phenolics. ‘Dingyuan’ had the largest content of phenolics, for the first time being reported higher than other common longan cultivars. Also, ‘Dingyuan’ exhibited more powerful competence in controlling redox reflected by the value of antioxidant potency composite index (ACI). There was a strong correlation between the abundance of polyphenols and antioxidant activity. In fifteen identified phenolic compounds, epicatechin was the richest present in all samples. Principal component analysis categorized different sources of longan into several groups, which might be a guidance for the layout of breeding programs, and for a proper processing strategy to longan pulp for better utilization of its natural advantages.