The present invention presents a novel class of compounds bis(triorganosilylalkyl) phosphites, e.g. bis(trimethylsilylmethyl) phosphite. The compound is readily prepared by the reaction of a corresponding triorganosilyl alkanol with phosphorus trichloride or by the partial hydrolysis of a corresponding tris(triorganosilylalkyl) phosphite with an equimolar amount of water followed by distillation of the reaction mixture.The compound has a remarkable anti-transplanted tumor effectiveness as established by the test with mice as the test animals for preventing the growth of Ehrlich's cancer cells and Sarcoma 180 cells. The compound has very low toxicity when orally administrated.