Multiple pharmacological activities were influenced of its activity of scavenging free radicals. The activity that different substituted theanine analogs at 5 position scavenge free radicals was studied in order to find the lead compound whose ability of scavenging free radicals was excellent. 7 kinds of analogs of theanine were synthesized via protection of phthalic anhydride, acylation and opening ring, deprotection of hydrazine hydrate from L-glutamic acid in the paper. The structures of the synthesized compounds was confirmed by IR,1H NMR and 13C NMR, and their activity of scavenging DPPH free radical and hydroxyl free radical were determined as well. The results indicated that the activity of scavenging free radical of 2-amino-5-((4-hydroxyphenyl)amino)-5-oxopentanoic acid was the best of the seven chemicals, whose rate of scavenging DPPH free radical was 90% at 0.002 mol?L-1 and rate of scavenging hydroxyl free radical was 95% at 0.004 mol?L-1. Followed was 2-amino-5-((4-aminophenyl)amino)-5-oxopentanoic acid. These showed that it could enhance the theanine ability of scavenging DPPH free radical and hydroxyl free radical that its 5 position was substituted by phenyl linking with nothing or electron donating group at 4 position. And the electron donating ability of group was stronger, the activity of scavenging free radicals was better.