In this study, a dichloromethane fraction (DCMF) from 70% Auricularia auricula-judae ethanol extract showed the highest level of antitumor activity compared to other solvent fractions (ethyl acetate, butanol, and water). The DCMF was found to have more potent antitumor activity against broncheoalveolar cancer (half maximal inhibitory concentration = 57.2 µg/mL) and gastric cancer cells (half maximal inhibitory concentration = 73.2 µg/mL) compared to the other solvent fractions, although all fractions inhibited the proliferation of the tumor cells in a dose-dependent manner. We further analyzed the DCMF composition by gas chromatography-coupled mass spectroscopy. Based on the results of this analysis, an antitumor active component (diazane) was identified in the DCMF. However, we found that diazane alone had a lower level of antitumor activity than the DCMF. These findings indicate that other unknown components of the DCMF also are responsible for the cytotoxic effects of DCMF against tumor cells. Semiquantitative reverse transcription polymerase chain reaction analysis demonstrated that DCMF induced cytotoxicity or tumor cell apoptosis as a result of the downregulation of Bcl-2 expression and p53 overexpression. Taken together, our study results demonstrated that the DCMF may be used as a functional additive for enhancing antioxidant activities and suppressing tumor growth in the body.