Gamma-tocotrienol (γT3) is an isoform of vitamin E found abundantly in palm oil, which is reported topossess antioxidant and anticancer activities. However, the immune-modulating properties of γT3 have yetto be elucidated. Breast cancer (BC) was induced in female BALB/c mice by injecting 4T1 murine mammarycancer cells into their mammary fat pads. When the tumour was palpable, the animals were randomlyassigned into two groups: (i) control [fed twice daily with 50 μl vehicle (soy oil)] or (ii) experimental (fedtwice daily with 50 μl of 0.5 mg of γT3). Results show that mice fed with γT3 had reduced tumour growthand metastasis. However, there are no marked changes in the percentages of peripheral blood leukocytes andcytokines production in these animals. Immunohistochemistry using antibodies to murine CD4, IL12Rβ2,IL24 and FoxP3 on tumour sections from γT3 treated mice suggested that γT3 induced suppression oftumour growth and metastasis as well as reduced immunosuppression in the tumour microenvironment.It can be concluded that, γT3 has the potential to suppress tumour growth and metastasis in this model.Further investigation on the host immune response is possible by prolonging treatment duration against BC.