This study presents a real- Time evaluation of tool flank wear detection system under wet machining based on electrical contact resistance. The developed tool wear detection system based on DC two terminal method uses the contact resistance between the tool and workpiece as a signal gauge to observe the progression of the tool wear during the cutting process. The contact resistance decreases as the increase of the flank wear contact area. Meanwhile, the influence of the thermo-electromotive force (E.M.F) is also measured and considered during the detection process. In the previous experiment, the target was the detection of the tool wear in face milling process, and also for uncoated solid square end mill by using a contact mercury transmission system. In this experiment, all attentions were focused on the new transmission system which is based on slip ring. The results of the experiment using the new slip ring transmission system on the present tool wear detection system based on DC two terminal method, demonstrates that the wear detection of the square end mill with indexable inserts has been done successfully under wet machining which was not possible in the previous system due to the isolation problem.,.