A bicycle hydraulic operating device is basically provided with a first base part, a second base part and a piston. The first base part includes a cylinder bore, a first end surface having a first opening, and a first passage extending from the first opening in the first end surface to the cylinder bore. The second base part includes a reservoir tank, a second end surface having a second opening, and a second passage extending from the second opening in the second end surface to the reservoir tank. The first end surface faces the second end surface. The first and second passages are fluidly connected via the first and second openings. The piston is movably disposed in the cylinder bore of the first base part.