In this paper, bilateral control system over networks is discussed and transmission delay issues are considered. This paper concerns on two subjects relating to transmission delay. The first one is how to realize real-time network transmission. Both systems; master and slave system run in RTLinux that is based on real time operating system. Thus, both systems should be connected to network device in real time as well. The other one is bilateral control system with transmission delay. In this paper, bilateral control system composed of disturbance observer and reaction force estimation observer is proposed. And the disturbance force from transmission time delay is compensated by disturbance observer. The validity of proposed control architecture is shown by experimental results.