The utilization of brittle materials is very popular in nowadays industry, such as free-form optics, semiconductor devices and MEMS components among many others. Unfortunately the machining difficulty blocks the further application of brittle materials in the advanced fields. The purpose of this paper is to investigate the machining capability of the diamond fly-cutting operation in grooving of brittle materials. The theoretical analysis of diamond fly-cutting technique was studied firstly. Then an experimental setup was established and the grooving experiment of mono-crystalline silicon, Bk7 glass and ceramics was performed. The results show that the fly-cutting of mono-crystalline silicon can achieve the best surface condition. The machining result of mono-crystalline silicon was also influenced by the feed rates. Better machining surface condition with fewer cracks can be obtained with less feed rates.