A novel nanoscale integrated all-optical diode is reported, realized by combining the strong plasmonic responses of gold nanoparticles with the all-optical tunable properties of polymeric photonic crystal microcavities. Non-reciprocal transmission properties are achieved based on the effect of surface-plasmon resonance enhancing the optical non-linearity and dynamic coupling of asymmetrical microcavity modes. An ultralow-threshold photon intensity of 2.1 MW cm(-2) and an ultrahigh transmission contrast over 10(4) are realized simultaneously. Compared with previously reported all-optical diodes, the operating power is reduced by five orders of magnitude, while the transmission contrast is enlarged by three orders of magnitude.