UBVRI photometry and low resolution optical spectroscopy of the type IIb SN 2011dh in M51 are presented, covering the first year after the explosion. The peak absolute magnitude in V-band of −17.12±0.18 mag indicates SN 2011dh to be a normal bright type IIb event. The peak quasi-bolometric luminosity indicates that ~ 0.06 M⊙ of 56Ni was synthesized in the explosion. The He I lines were detected in the spectra much before the maximum light in B-band. The nebular spectra of SN 2011dh show a box shaped emission in the red wing of [OI] 6300, 6363 line due to Hα emission excited because of shock-wave interaction. The analysis of the nebular spectra indicates a progenitor with a main sequence mass of 10-15 M⊙.