Abstract: OBJECTIVE To investigate the inhibition of mice’s Lewis lung cancer from the polysaccharides and alkaloid extracted from fresh Dendrobium candidum, and reveal the anti-tumor mechanism. METHODS Lewis tumor-bearing mice models were established. Mice were divided into eight groups: model group, cyclophosphamide(CTX)group, high(20 g·kg^?1), middle(10 g·kg^?1) and low(5 g·kg^?1) dose of polysaccharides extracted from fresh Dendrobium candidum, high(20 g·kg^?1), middle(10 g·kg^?1) and low(5 g·kg^?1) dose of alkaloid extracted from fresh Dendrobium candidum. CTX group was injected intraperitoneally with CTX(40 mg·kg^?1) on day 3, 6 and 9 following the administration started, the other groups were given successively for 20 days, then the effects of polysaccharides and alkaloid extracted from fresh Dendrobium candidum on tumor growth, spleen indexs, interleukin-2 (IL-2) and tumor necrosis factor-α(TNF-α) levels were determined. RESULTS Compared with model group, the tumor weight in different doses of polysaccharides and alkaloid groups was lower. The tumor weight could be obviously inhibited in high dose of polysaccharides, high and middle dose of alkaloid(P<0.05). Spleen weight and spleen index in different doses of polysaccharides and alkaloid groups were higher than that in control group. That effect was remarkable in high and middle dose of polysaccharides(P<0.05). Different doses of polysaccharides and alkaloid groups could elevate TNF-α and IL-2 levels. The levels in high dose of alkaloid, high and middle dose of polysaccharides groups increased obviously(P<0.05). CONCLUSION The polysaccharides and alkaloid extracts from fresh Dendrobium candidum can obviously inhibit the growth of transplanted Lewis tumor, and the mechanism may be related to improve spleen index and the regulation of TNF-α and IL-2 expression.