Tearing instability is shown to be greatly enhanced by ambipolar diffusion near the locations where two-dimensional magnetic fields reverse signs. The growth time is found to be on the order of the ambipolar diffusion timescale, independent of electrical resistivity. Consistent with the earlier works, the enhancement in the reconnection of field lines indeed arises from the development of a singular current perturbation. Such magnetic reconnection is driven by the steepening effect of ambipolar diffusion on the magnetic fields near the held-reversal lines. Although the background magnetic fields are evolving on a similar timescale as the perturbations, we show that magnetic reconnection proceeds substantially faster than the steepening of the background fields. In contrast to the conventional tearing instabilities in three dimensions, where the magnetic reconnection occurs only in the flux surfaces that contain the free energy, a positive Delta', the three-dimensional extension of this new tearing instability can occur only in regions where the Lorentz force reverses the sign. This report outlines how the three-dimensional reconnection may proceed in a similar fashion as the two-dimensional counterpart does.