Actively mode-locked fiber lasers that are stabilized with a highly nonlinear photonic crystal fiber are proposed. The nonlinear polarization rotation effect of the photonic crystal fiber is theoretically analyzed, and the stabilization mechanism of short pulse lasing is explained. Stable pulse output with a pulse width of about 44 ps and a repetition rate of 5 GHz is a thieved experimentally. The proposed stable fiber laser can be used in an OCDMA system.