Abstract: An improved tooth profile for compressor screw rotors is disclosed. In the tooth profile, the following-side first curve of the male rotor is generated using a generation parameter of a quadratic function f(x)=a.sub.10 x.sup.2 +b.sub.10 x+c.sub.10 whose constants are optimized to meet specified constraint conditions. The above constraint conditions include an increased pressure angle for achieving good cutting condition of the rotors, a sealing surface suitable for minimizing the negative torque applied to a following rotor due to the gas pressure in the trapped pocket volume defined between the rotors, a large surface contact between the two rotors for improving the sealing effect as well as the durability of the rotors, and a minimized specific sliding at the driving force transmission part of the rotors for reducing the operational vibration and noise of the rotors.