A dietary deficiency of tryptophan can cause pellagra and lead to low levels of serotonin that is associated with depression, aggression, anxiety and overeating in humans. Thus, enhancement of tryptophan content in rice has great potential benefit for human and animal diets. In this study, a total of 1,350 rice mutant population was used to identify single nucleotide polymorphisms (SNPs) in Oryza sativa anthranilate synthase alpha1(OASA1) gene that was associated with negative feedback in tryptophan biosynthesis. For high-throughput TILLING analysis, 5 fluorescence-labeled primer sets were designed to cover exon regions of OASA1 locus and PCR amplifications were analyzed using ABI3130xl DNA sequencer. Through the screening of 1,350 mutant lines, nine mutant lines produced one or two cleaved fragments in the PCR products of OASA1 locus. The full sequencing of nine mutant lines revealed that total 31 SNPs were located in the regions of OASA1. In particular, three mutant lines contained SNPs in coding regions that resulted in an amino acid change. The tryptophan contents of the three mutant lines were 2.2- to 2.3-fold higher than the wild type. These high-tryptophan mutant lines will be used rice breeding programs and contribute directly to enhancing human nutrition.