Stabilities of nitrenium ions estimated by in silico analyses and in vitro and in vivo genotoxicity were compared for four aniline derivatives, 2-chloro-4-methylaniline (2C4MA), 4-chloro-2-methylaniline (4C2MA), 2-chloro-4,5-difluoroaniline (2C4,5DFA) and 4-trifluoromethylaniline (4TFMA). The AM1 values as an index of stability of the nitrenium ions of 2C4MA, 4C2MA, 2C4,5DFA and 4TFMA were -5.38, -4.67, 8.36 and 16.6 kcal/mol, respectively, indicating that the potential of mutagenicity is high for 2C4MA and 4C2MA and low for 2C4,5DFA and 4-TFMA. The specific mutagenicity determined in Ames tests with S9 mix for 2C4MA and 4C2MA was 4,067 and 12,500 revertants/mg/plate, respectively. The specific mutagenicity could not be determined for 2C4,5DFA because the results of the Ames tests were equivocal. Among the four aniline derivatives, only 4TFMA showed positive results with and without S9 mix in the Ames tests and the specific mutagenicity of 4TFMA were 1,590 and 1,910 revertants/mg/plate for TA100 with and without S9 mix, respectively. These results indicated that the mutagenic potential is high for 2C4MA and 4C2MA and is low for 2C4,5DFA and 4TFMA. In vivo genotoxicity is positive for 2C4MA, 4C2MA and 2C4,5DFA and is negative for 4TFMA. The results of in silico analyses and in vitro and in vivo genotoxicity tests were consistent for aniline derivatives with strong mutagenicity (2C4MA and 4C2MA) but were not for those with weak mutagenicity (2C4,5DFA and 4TFMA). Careful assessment for the risk of carcinogenicity is necessary for aniline derivatives with weak mutagenicity by combining in silico analyses and in vitro and in vivo genotoxicity tests.