Brucea javanica is a traditional herbal medicine in China, and its antitumor activities are of research interest. Brucea javanica oil, extracted with ether and refined with 10% ethyl alcohol from Brucea javanica seed, was used to treat hepatoma H22-bearing mice in this study. The antitumor effect and probable mechanisms of the extracted Brucea javanica oil were studied in H22-bearing mice by WBC count, GOT, GPT levels, and western blotting. The H22 tumor inhibition ratio of 0.5, 1, and 1.5 g/kg bw Brucea javanica oil were 15.64%, 23.87%, and 38.27%. Brucea javanica oil could inhibit the involution of thymus induced by H22 tumor-bearing, but it could not inhibit the augmentation of spleen and liver. Brucea javanica oil could decrease the levels of WBC count and GOT and GPT in H22-bearing mice. The protein levels of GAPDH, Akt, TGF-β1, and α-SMA in tumor tissues decreased after being treated with Brucea javanica oil. Disturbing energy metabolism and neoplastic hyperplasia controlled by Akt and immunoregulation activity were its probable antitumor mechanisms in hepatoma H22-bearing mice.