To provide an improved cap for high voltage ignition plug, with which it is possible to mount and connect the plug on/with an internal combustion engine simply and certainly.

A cap concerned 20 for a high voltage ignition plug is composed of a cord cap part 29, rain cover 21, and a female type plug terminal 34 consisting of a resilient contacting piece 36 capable of compressive deformation along the center of axis A of a high voltage cord 5 wherein an engaging recess 39 is formed at the inside surface near the top end of an engine hole 1, and a resilient fixture member 24 is held at the periphery of the cord cap part 29 in a position nearer the female plug terminal 34 than the engaging recess 39, and a receptacle seat 32 is formed protrusively to allow the engaging recess 39 to engage a detent pawl 28 provided on the resilient fixture member 24. Accordingly the operation of mounting the cap 20 consists of intrusion with a light force including the process that the bottom end face of the above- mentioned cord cap part 29 is fitted in a groove carved at the top end face of a resilient cap part 38, wherein the completion of the fitting operation can easily be known from the clicking sound generated when the pawl 28 is engaged by the engaging recess 39.