In vitro skin iritation of anti-inflammatory drugs was investigated in terms of the cytotoxicity method to human skin fibroblast cells. Five anti-inflammatory drugs (Diclofenac, Naproxen, Meclofenamic acid, Ibuprofen and Fnoprofen) which are commercially available as oral preparations or injections were tested. The cytotoxicity of 5 chemicals was evaluated by using MTT[tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay. NRU (neutral red uptake) assay and Alamar Blue assay after fibroblast cells had been exposed to the chemicals for 24 hours or 489 hours. The $IC_{50}$ values of the chemicals showed the comparative strength of cytotoxicity as following order of Meclofenamic acid>Diclofenac>Fenoprofen>Ibuprofen>Naproxen. The values of $IC_{50}$ determined by Alamar Blue assay were lower than those of MTT and NRU assay. These data suggest Alamar Blue assay can be useful method for assessing in vitro skin irritation potential of anti-inflammatory drugs.