A bicycle bottom bracket assembly is at least provided with a first support member and a first bearing unit. The first support member includes a first hanger mounting part and a first bearing mounting part. The first bearing unit is coupled to the first bearing mounting part. The first hanger mounting part has a first outer circumferential surface that is configured and arranged to be press-fitted into a first open end of a hanger part of a bicycle frame. The first hanger mounting part has a first slit extending in an axial direction relative to a rotational axis of the first bearing unit from an open axial innermost end of the first slit at least up to a region that is located radially outwardly from the first bearing unit in a radial direction relative to the rotational axis of the first bearing unit.