The compositions of amino acid in 6 monocultured benthic diatoms used in aquaculture of Haliotis discus hannai were analyzed, and effects of 15 artificial synthetic amino acids on the settlement and metamorphosis of H. discus hannai larvae. Results showed that the content of L-aspartic acid was highest in all diatoms, and that of L-glutamic acid was second high. In experiment using settlement slat without benthic diatom attached, the highest settlement rate (33.3 ${pm}$ 8.8%) was obtained with L-glutamic acid, and a higher value (16.7 ${pm}$ 3.3%) was found with L-aspartic acid at 24 h after experimental commencement, compared to that of control (8.6 ${pm}$ 5.1%). 80 h later the metamorphosis rates of L-glutamic acid (86.7 ${pm}$ 10.7%) and L-aspartic acid (80.0 ${pm}$ 3.3%) groups were higher than control group(0) and other amino acids significantly. The response rate of L-glutamic acid was the highest (62.0%), and those of L-aspartic acid (30.0%) and L-threonine (25.3%) groups were also significantly higher than control group. In the experiment using settlement slat with benthic diatom attached, the best effect of various amino acids on induction of larval settlement was obtained with L-glutamic (82.0 ${pm}$ 6.9%) and L-aspartic acid (78.7 ${pm}$ 5.1%) at 24 h after experimental commencement. The settlement rates of L-histidine, L-leucine, L-lysine, L-methionine, L-phenylalanine, and L-tyrosine groups were significantly lower than control group. The same differences in the metamorphosis rate at 56 h after experimental commencement and in the response rate were found. It should be noted that after 80 h the metamorphosis rates of L-histidine (74.0 ${pm}$ 12.0%) and L-lysine (87.0 ${pm}$ 8.8%) declined rapidly compared to those of 56 h (8.0 ${pm}$ 12.0%; 7.7 ${pm}$ 12.0%).