Abstract: Baryon acoustic oscillations (BAO) in large galaxy surveys can provide an excellent standard ruler test to measure the cosmological distance scale, such as the angular diameter distance and the Hubble parameter, and therefore dark energy properties. This requires that we understand all of the physical effects that could alter the acoustic feature during the nonlinear evolution of structure. There are two important aspects of the nonlinear effects on BAO. First, the BAO signature is gradually reduced with time and in scale due to nonlinear growth of density fields, redshift distortions, and galaxy bias. Second, the various nonlinear effects may alter the observed BAO scale at low redshift, relative to the linear acoustic scale derived from the CMB, which would result in biased estimation of dark energy parameters. In this talk, I will present effects of such nonlinearities on BAO from N-body results: nonlinear growth and redshift distortions degrade the contrast of BAO while shifting BAO less than ~0.5% at z=0.3. I will show that most of these nonlinear effects can be reversed by a simple reconstruction scheme.I will also discuss the effect of galaxy bias on BAO.