The most effective drugs based on the type of cancer are chosen for chemotherapy. Tumor cells can be targeted at the DNA, RNA or protein level, and most of the classical anticancer drugs interact with tumor DNA in a time-dependent manner or a concentration-dependent manner. However, it has been unclear to date whether a combination therapy is carried out by using exact classification. Thus it is necessary to reclassify a great number of anticancer drugs. We propose a new classification system based on pharmacological effects of anticancer drugs. Classification of four anticancer drugs (cisplatin, carboplatin, paclitaxel and gemcitabine) was performed by the 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. The four anticancer drugs were grouped by IC50 values (inhibitory concentration, 50%) in a time-dependent manner and a concentration-dependent manner. The present approach may be combined to enhance the chemosensitivity, improve the dose of cytotoxic drugs and evaluate the effects of novel anticancer drugs.