Titanium alloys have been extensively used in aerospace industries and account for almost 30 wt% of materials used in an aerospace engine. Surface integrity of machined titanium components has a significant effect on reliability and sustainability those components in aer-ospace industry. Surface integrity could be affected by process parameters, cooling condi-tions and the wear level of the tools used in machining. An important example is the surface integrity of the holes drilled in titanium alloy Ti6Al4V. Although previous studies have shown that tool wear and cutting parameters influence surface integrity and burr formation, little work has been published about the effect of drill wear on the surface integrity and burr formation in drilling of titanium alloys in detail. In this study the influence of tool wear and use of coolant on surface integrity and burr formation in drilling of Ti6Al4V has been inves-tigated by metallographic study and micro hardness measurement of the material adjacent to holes drilled on plates of Ti6Al4V with drills of various wear levels and at three different cutting conditions. Micro structural and micro hardness alteration in drilled holes at the hole entrance, in the middle of the hole and at the hole exit as well as burr formation have been analyzed for the tool wear levels 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mm. The tests were carried out in vertical direction without coolant and horizontal and vertical directions with coolant. The results show that limiting the wear level on the drills and use of coolant significantly lower the burr formation and microstructural alterations. Higher tool wear levels increase the depth of micro structural deformation, micro hardness and burr heights. These differences are not significant for wear levels up to 0.4 mm irrespective of cutting conditions but increase sig-nificantly when tool wear level exceeds 0.6 mm.