The　cytotoxicities　of　biphenyl,　2-bromine　biphenyl,　biphenyl-2-carboxylic　acid　and　2-amino　biphenyl,　and　the　synergy　toxicities　of　the　four　different　substituted　biphenyl　compounds　with　single-walled　carbon　nanotubes　(SWNTs)　were　investigated　with　MTT.　Results　show　that　the　cytotoxicities　of　the　four　compounds　were　different　and　dependent　on　time　and　concentrartion.　The　cytotoxicity　in　decresing　order　are　2-aminobiphenyl,　2-bromine　biphenyl,　biphenyl,　and　biphenyl-2-carboxylic　acid.　In　the　synergy　toxicity　experiments,　the　cytotoxicity　was　enhanced　for　2-3　times　when　the　biphenyl　compounds　combined　with　SWNTs,　indicting　that　biphenyl　compounds　combined　with　SWNTs　resulted　in　their　synergy　toxicity.