We report the photo-pumped lasing action from a very small oxide-confined 870-nm vertical microcavity lasers with high-contrast AlGaAs-AlxOy mirrors. The effective cavity length is as small as 0.37 mu m, and the oxide aperture size is 0.74 mu m, estimated from the blue-shift of lasing mode due to the lateral confinement. The observed blue-shift of the lasing mode is 13.4 nm, the largest one ever reported for vertical cavity lasers. The optical losses seem to be size-independent for these small microcavity lasers. Our results indicate the possibility of the ultimate microcavity of order of lambda(3).