Recent development in string theory has led to the extension of General Relativity, i.e. Stringy Gravity. It postulates the entire closed string massless sector to be geometric and thus gravitational. I will first introduce the mathematical foundation and then discuss the solution to dark matter/energy problems. In terms of R/(MG), i.e. the dimensionless radial variable normalized by mass, Stringy Gravity agrees with General Relativity near infinity, but modifies it at short distance. At far short distance, gravitational force can be even repulsive. These may solve the dark matter and energy problems, as they essentially arise from small R/(MG) observations: far distance divided by much heavier mass.