The chlorophenol chemicals(CPs) are a major class of widely distributed and frequently occurring persistent environmental pollutants. Pentachlorophenol (PCP) has been proposed to be procarcinogen in rodents and in possibly human beings. Human beings also easily expose to other chlorophenol chemicals, including 4-chlorophenol (CP), 2,4-dichlorophenol (DCP),2,3,4-trichlorophenol(TCP), prompting this investigation of their comparative cytotoxic effects and cell death mechanisms, assayed in fibroblast L929 cells, The effective concentration for half-maximal response (EC50) values at 24 h for CP, DCP, TCP, and PCP are 2.18, 0.83,0.46, and 0.11 mmol/L respectively and the EC50 values at 48 h are 1.18, 0.13, 0.08, and 0.06 mmol/L respectively by using 3-(4,5-dimethylthiazd-2-yl)-2, 5-diphenyltentrazolium bromide (MTT) reduction assay. A clear structure-activity relationship was observed between toxicity of CPs and their octanol-water partition coefficients. The further studies indicate that CP, DCP, and TCP induce apoptosis in L929 cells in a concentration or time-dependent manner, but PCP mediates cell death more characteristic of necrosis than apoptosis. These results not only demonstrate that L929 cell growth inhibition bioassay may be useful to provide the comparative evaluation of toxicity of CPs in vitro, but also implicate that CP, DCP, TCP, in comparison with PCP, can induce L929 cell death by apoptosis, resulting in lower procarcinogensis, which may help to elucidate the molecular basis for the adverse health effects associated with CPs exposure.