Hydraulic systems are of great advantages to high-frequency controlling and high-efficient energytransforming as power transmissions. The prime characteristic is to use hydraulic fluid as lubricant. Hydraulic equipment consists of many bearing/seal parts and its performance depends deeply on them. For improvement of performance of hydraulic systems, it is important to clarify the behavior of their 'tribology' . In our society, the Japan Hydraulics and Pneumatics Society (JHPS), we have been organizing continuously the research committees on tribology and investigating on it. We built test apparatuses and studied experimentally. Also we reviewed the domestic and overseas papers on tribology and discussed them. In this report, we will introduce our activities and researches on tribology of hydraulic equipment, discuss these problems, and mention the trends and the future.