More commonly considered criteria for judging the machinability are the cutting forces on the tool and power consumption. A classical Merchant’s model is widely used to predict the cutting forces while machining isotropic material. However no such model exists to predict the cutting forces while machining orthotropic materials. In this paper an effort is made to modify the Merchant’s formula by incorporating the K-factor to evaluate the shear strength, the fiber orientation as shear angle and a constant coefficient of friction. The cutting forces evaluated by modified Merchant’s model on unidirectional GFRP composite material has been compared with the results predicted by two-dimensional FEA model. In FEA model both maximum stress and Tsai-Hill failure criteria were used to simulate the chip separation. The influence of composite design, in particular the fiber proportion and orientation on cutting forces has been investigated. The higher fiber proportion of the composite results in increased cutting forces. Fiber angles 450 and 600 have shown favorable results. The predicted principal cutting forces by FEA agree well with the results evaluated by modified Merchant’s model.