The interwell coupling effects on the small-signal response of unstrained multiple quantum well (MQW) lasers have been studied theoretically. However, in the previous study the transition matrix element of an isolated QW was assumed. The rate equations are solved again for the intensity modulation response but including a matrix element of a coupled double QW (DQW), and then the results are compared with the previous ones to confirm that the former study assumption, referred above, does not make any significant qualitative difference for the example that we have been considering; and also, as it is advantageous to reduce computational time, it was used to calculate the frequency and damping rate of the relaxation oscillations. Results and discussion for these characteristics of a GaInAsP-InP DQW laser are presented as a specific example. We conclude that, in contrast to the common belief, the coupling effect can enhance the modulation characteristics under certain conditions.