Gravitational microlensing is a powerful tool to study the Galactic halo dark matter and the Galactic bar structure. If a massive compact object, like a star, perfectly aligns along the line of sight toward the back ground source star, the light from the source is bent by the gravitational field of the lens object and the source brightness is magnified, called microlensing. If the Galactic halo dark matter consist of so-called Massive Compact Halo Objects (MACHOs), like white dwarf, brown dwarf or primordial black hole, they can be detected by microlensing observation toward the Large Magellanic Cloud. While the fraction of MACHOs in our dark halo has been constrained less than 15% by observations, the existence of MACHOs themselves are still controversial. The microlensing events are also routinely observed toward the Galactic bulge region. The event rate of microlensing can prove the structure of the bulge. Current observations show that our galaxy has a bar structure. Detail modeling of baryonic matter density can constrain the dark mater density profile in the Galactic central region.