Abstract The formation of the compound, ((CH3)3 Sn)2O·(CH3)3Sn X, H2O, from trimethyltin halide by the action of sunlight in the presence of air have been studied and the mechanisms of the formation were interpreted. Identical products have been prepared by the following methods: (A) By oxidizing of trimethyltin group along with trimethyltin halide in benzene solution in the dark, and (B) by treating two molecular proportions of trimethyltin hydroxide with one molecular proportion of trimethyltin halide in hot benzene solution. 2. Compounds exhibit salt–like properties, being readily soluble in water, alcohol, acetone and liquid ammonia, and insoluble in benzene and ether. They conduct electric current appreciably in their solutions. 3. When the liquid ammonia solution is treated with an equivalent amount of metallic sodium in respect to the iodine trimethyltin oxide, ((CH3)3Sn)2O, and trimethyltin group, (CH3)3Sn, are produced. 4. Compounds of the type, ((CH3)3Sn)2O·HX, H2O, have been prepared by treating of one molecular proportion of trimethyltin hydroxide with one molecular proportion trimethyltin halide or one molecular proportion of trimethyltin oxide with one molecular proportion of halogen acid under suitable conditions. 5. They are salt–like properties, being soluble in water and alcohol, and insoluble in nonionizing solvents such as benzene and ether. 6. Their melting points and stabilities are higher than those of the type, ((CH3)3Sn)2O·(CH3)3Sn X, H2O.