High-speed machining of titanium alloys generates high cutting temperature in the cutting zone, which decreases tool life rapidly. So the improvement of the tool life in the high-speed machining of titanium alloys very much depends on the effectiveness of the cooling/lubrication provided. In this paper, coated cemented carbide tools were used in high-speed end milling of Ti-6Al-4V. Experiments were conducted under various cooling/lubrication conditions to find the optimal cooling/lubrication condition to improve the tool life. Dry, flood coolant, nitrogen-oilmist, compressed cold nitrogen gas (CCNG) at 0, and -10 โข C, and compressed cold nitrogen gas and oil mist (CCNGOM) as the cooling/lubrication conditions were studied. For this research, a new cooling system was used to lower the temperature of compressed nitrogen gas. The experimental results show that the cooling/lubrication condition for CCNGOM provided the best tool life among all the cooling/lubrication conditions employed. SEM analysis was carried out on the worn tools to determine tool failure modes and wear mechanisms. Flank wear was the dominant failure mode under the cooling/lubrication conditions, including dry, nitrogen-oil-mist, CCNG and CCNGOM. Excessive chipping at the cutting edge and fracture on the flank face were responsible for tool failure under flood coolant condition. Analyses based on SEM suggest that diffusion wear and thermal fatigue wear were the predominant wear mechanisms of the coated tools under the cooling/lubrication conditions employed.