Abstract: A protective boot for preventing contamination of the oil in a hydraulic piston-cylinder assembly consists of an elongate flexible sleeve having a first end removably securable to the head of the cylinder and a second end removably securable to the distal end of the piston rod. The boot is split along a longitudinal seam which can be closed by a zipper, a hook and loop type fastening strip, or other suitable attachment devices. Several flexible metal or plastic stays encircle the sleeve at spaced locations to prevent the sleeve from contacting the piston rod. Each stay is split to accommodate the seam.