The present invention provides method 1 for producing a trialkyl gallium comprising the steps of reacting gallium, magnesium, and an alkyl halide in an ether, and diluting during the reaction the reaction system with an ether; method 2 for producing a trialkyl gallium comprising the steps of heating in a vacuum a mixture of magnesium and molten gallium, and reacting the mixture with an alkyl halide in a solvent; and method 3 for producing a trialkyl gallium comprising the step of reacting an alkyl metal with an alkylgallium halide compound represented by the formula Ga2RmX6-m wherein R is a methyl or ethyl group, X is a halogen atom, and m is an integer from 1 to 5.