Cancer patients seek alternative remedies such as traditional medicinal plants for safe and effective treatment and help overcome the side effects of conventional therapy. Current knowledge indicates that extracts of Strobilanthes crispus of the Acanthaceae family exhibit potent anticancer properties in vitro and are non-toxic in vivo. S. crispus was also reported to be protective against chemical hepatocarcinogenesis. We previously showed that a bioactive fraction of S. crispus leaves also synergized with tamoxifen to cause apoptosis of human breast cancer cell lines without damaging non-malignant epithelial cells. The present study aimed to evaluate the antitumor effect of S. crispus dichloromethane fraction (F3) using N-methyl-N-Nitrosourea (NMU)-induced rat mammary tumor model. Tumor regression was observed in 75% of the rats following 8-week oral administration of F3 with no secondary tumour formation and no signs of anemia or infection. However, no improvement in the liver and renal function profiles was observed. Major constituents of F3 were identified as lutein, 131-hydroxy-132-oxo-pheophytin a, campesterol, stigmasterol, β-sitosterol, pheophytin a and 132-hydroxy-pheophytin a. These compounds however, may not significantly contribute to the antitumor effect of F3.