To develop environmentally friendly hydraulic components which utilize environmentally compatible fluids as a transmitting media, preliminary studies were conducted. Various PVD coatings were deposited on hydraulic components, and their chemical and mechanical properties were investigated by AES, SEM, XRD, nanoindentation test, and scratch test. The tribologocal properties were also evaluated by high speed wear test. The hardness of Cr-Si-N coatings gradually increased with increasing Si content and reached the maximum value of approximately 24GPa at the Si content 9.8 at. %. This value is approximately 1.6 times higher than that of the CrN. Much improved friction behavior was observed under tap water environment without delamination or surface cracking up to 1600 rpm by applying Cr-Si-N coating on the AISI 4340 cylinder barrel. Even an initial decrease in the friction coefficient at the starting and low rpm region was resulted, and this improvement was accompanied by friction mode change from adhesive mode to abrasive mode.