Forced convection from a heated cylinder performing rotational oscillation about its own axis and placed in a uniform stream is investigated. The governing equations of motion and energy are solved numerically to determine the flow field characteristics and the heat transfer coefficients. The main dominating parameters are Reynolds numbers, Re, Prandtl number, Pr, amplitude of oscillation, Theta(A), and the frequency ratio, F-R, which represents the ratio between the frequency of oscillation, f, and the natural frequency of vortex shedding, f(0). The ranges considered for these parameters are 40 less than or equal to Re less than or equal to 200, 0 less than or equal to Theta(A)less than or equal to pi and 0 less than or equal to F(R)less than or equal to 2, while the Prandtl number is kept constant at 0.7. The lock-on phenomenon has been detected and its effect on the thermal field has been determined. The results show that the lock-on phenomenon occurs within a band of frequency near the natural frequency and the heat transfer coefficient has shown appreciable increase in the lock-on frequency range.