Abstract. Optical UBVRI photometry and medium resolution spectroscopy of the type Ib supernova SN 2009jf, during the period ∼ -15 to +250 days with respect to the B maximum are reported. The light curves are broad, with an extremely slow decline. The early post-maximum decline rate in the V band is similar to SN 2008D, however, the late phase decline rate is slower than other studied type Ib supernovae. With an absolute magnitude of M_V = -17.96±0.19 magnitude at peak, SN 2009jf is a normally bright supernova. The peak bolometric luminosity and the energy deposition rate via ⁵⁶Ni →⁵⁶Co chain indicate that ∼ 0.20^+0.03_-0.03 M_⊙ of ⁵⁶Ni was ejected during the explosion. He I 5876&AA; line is clearly identified in the first spectrum of day ∼-15, at a velocity of ∼ 16000 km s^-1. The [O I] 6300-6364 &AA; line seen in the nebular spectrum has a multi-peaked and asymmetric emission profile, with the blue peak being stronger. The estimated flux in this line implies ≥ 1.3 M_⊙ oxygen was ejected. The slow evolution of the light curves of SN 2009jf indicates the presence of a massive ejecta. The high expansion velocity in the early phase and broader emission lines during the nebular phase suggest it to be an explosion with a large kinetic energy. A simple qualitative estimate leads to the ejecta mass of M _ej = 4 - 9 M_⊙, and kinetic energy E _K = 3 - 8 × 10⁵¹ erg. The ejected mass estimate is indicative of an initial main-sequence mass of ≥ 2 - 25 M_⊙