Butt welds were carried out on Ti-6Al-4V sheets with thickness 1.7 mm using a 2.2 kW CO2 laser welding. The effect of linear heat input on the joint geometry, microstructure and mechanical properties was investigated. The welding process efficiency and the ratio of root width to top width were used to evaluate the joints. The results showed that fully penetrated joints were achieved at linear heat input of greater than 4.00 J/mm. Metallographic observations showed that fusion zone (FZ) consists of acicular α′ phase within prior coarse β grains. Increasing linear heat input causes to change the martensitic phase from an acicular like to plate like morphology. Also, the prior β grain size increases because longer time exists for β grain coarsening. The microhardness values in the FZ decrease with increasing the linear heat input. This phenomenon can be attributed to decrease of martensitic phase formation in the FZ. The ultimate tensile strength of the joints ranges from 624 to 1002 MPa at room temperature.
