A hydraulic operating device for a small vehicle including a bicycle is basically provided with a base member, an operating member, a piston, a handlebar fixing structure and a hydraulic reservoir tank. The base member includes a cylinder having a cylinder bore. The operating member is pivotally coupled to the base member about a pivot axis. The piston is movably disposed in the cylinder bore and operatively coupled to the operating member to move the piston within the cylinder bore. The handlebar fixing structure is coupled to the base member. The handlebar fixing structure defines a handlebar arrangement area. The hydraulic reservoir tank has a hydraulic fluid chamber fluidly connected to the cylinder bore. The hydraulic reservoir tank at least partially overlaps the handlebar arrangement area as viewed in a pivot axis direction parallel to the pivot axis of the operating member.