A simple method to measure the intracavity losses of the single frequency laser utilizing the resonant relaxation oscillation (RRO) frequency and output power is presented. By analyzing the dependence of the RRO frequency on the output power, the theoretical function of the intracavity losses is presented. Substituting the measured output power and RRO of the single frequency Ti:sapphire laser into the theoretical function, its intracavity losses is obtained.