Recent studies about variable nozzles, that are a rectangular type nozzle and an axisymmetric type nozzle, of the precooled turbojet engine (S-engine) which are developed for the demonstration of the key technologies for the propulsion system of the hypersonic airplane and the first stage propulsion of the TSTO space plane are described in this paper. For the rectangular nozzle, three types of C-shaped carbon/carbon composite cowls which includes subscale model of the precooled turbojet engine are fabricated and the fine attachment to the ramp is confirmed. For the firing of the S-engine, stainless steel cowl with concrete heat insulator are fabricated and tested for 20 sec. Axisymmetric variable plug nozzle which is made of C/C material is fabricated and pressurized by the cold flow test. The axisymmetric plug nozzle can be operative up to 0.57 MPa of nozzle inlet pressure.