An optical sensor module is provided in which an engagement portion of a board unit is fitted in a groove of an optical waveguide unit and, even with the single engagement portion, the board unit is stably supported. An optical sensor module includes an optical waveguide unit, and a board unit mounted with an optical element and coupled to the optical waveguide unit. The optical waveguide unit includes a single edge extension portion axially extending along one side edge of an over-cladding layer, a board unit engagement groove provided in the single edge extension portion, and a projection provided on a side wall of the vertical groove and kept in abutment against an engagement portion of the board unit. The board unit includes an engagement portion fitted in the vertical groove, which abuts against the projection within the vertical groove.