We report a Q-switched Nd:YAG laser using a dual-cavity configuration which enables the pulse width to be varied between 24 ns and 32 ns. We used a LiF:F-2(-) color-center crystal for passive Q-switching and an auxiliary cavity for lasing the emitted light from the LiF:F-2(-) crystal. The lasing in the auxiliary cavity causes the LiF:F-2(-) to reclose and a tail of the Q-switched pulse to be cut out. The rate equations were used to investigate the output characteristics from a Q-switched laser with a dual-cavity configuration. The experimental results were in good agreement with the results of the theoretical simulation.