A bicycle disc brake caliper assembly is basically provided with a main caliper body, at least one brake pad and a mounting adapter. The main caliper body includes a first coupling portion that is configured not to be directly attached to a bicycle frame. The at least one brake pad is movably attached to the main caliper body. The mounting adapter includes a second coupling portion that is configured to be detachably coupled to the first coupling portion, and a mounting portion that is configured to be mounted to a bicycle frame.