A method of manufacturing an optical sensor module which eliminates the need for the operation of alignment between a core in an optical waveguide section and an optical element in a substrate section, and an optical sensor module obtained thereby. An optical waveguide section W1 including groove portions (fitting portions) 4a for the positioning of a substrate section, and a substrate section E1 including fitting plate portions (to-be-fitted portions) 5a for fitting engagement with the groove portions 4a are individually produced. The fitting plate portions 5a in the substrate section E1 are brought into fitting engagement with the groove portions 4a in the optical waveguide section W1 whereby the substrate section E1 and the optical waveguide section W1 are integrated together.