Abstract: Tumorous cells are characterized by distinctive metabolic reprogramming and living conditions. Understanding drug metabolizing features in tumor cells will not only favor the estimation of metabolic rate, elimination half life and the assessment of potency, but also facilitate the optimal design of anti-tumor drugs/prodrugs. This article reviewed the expression and activity features of major drug metabolizing enzymes (DMEs) in solid tumorous tissues, such as liver, intestine, breast and lung, and the difference from the correspondingly normal tissues, exemplified by the metabolic properties of some classic antitumor-agents in tumorous tissues. In combination with the data retrieved in vitro tumor cell lines, we discussed the similarities and differences of DMEs expression and function between tumor tissues (in vitro) and tumor cells (in vitro), and proposed the possible factors that cause the differences.