In this paper, numerical investigation of the effects of cutting conditions in slot up milling of Ti-6Al-4V is conducted using Finite Element Method (FEM). Experiments are conducted to validate the FEM models. The validated models are then used to predict the cutting force components when different cutting conditions are applied. It is found that cutting speed, feed rate, and depth of cut have strong influence on cutting force components and tool temperature. This research provides insightful guidance for selecting optimal cutting conditions for slot milling of Ti-6Al-4V.