  MASTER OT J120451.50+265946.6 (M12045), discovered by the MASTER Global
Robotic Net, is a Type Ib supernova (SN) that exploded in NGC 4080. We present
the {\it BVRI} photometric and spectroscopic observations upto $\sim$250 days
since $B_{max}$. At the time of discovery the SN was a few weeks past maximum
light and our observations capture the linearly declining light curve phase.
M12045 declines faster as compared to SNe 1999dn and 2009jf at comparable
epochs. Rigorous spectroscopic monitoring reveals that M12045 is a normal Type
Ib SN. The analysis of the nebular phase spectra indicates that $\sim$ 0.90
M$_\odot$ of O is ejected in the explosion. The line ratio of [\ion{O}{I}] and
[\ion{Ca}{II}] in the nebular phase supports a massive WR progenitor with main
sequence mass of $\sim$ 20 M$_\odot$.
