In this work, we outline the synthesis of binary semiconductor heterojunction comprising of two dimensional Graphene oxide loaded with NiO nanoparticles in varying amounts, by an in-situ method under controlled atmosphere. X-ray diffraction (XRD), resonant Raman spectroscopy, FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis diffuse reflectance (DR) spectroscopy and photoluminescence (PL) spectroscopy were used to characterize the as-synthesized nanocomposites. The results indicated that the p-n heterojunction is formed between the cubic structured NiO and GO in the NiO/GO nanocomposites. Moreover, the photocatalytic activity of the as-prepared NiO/GO nanocomposites for the degradation of Methylene blue (MB) was much higher than that of as-prepared cubic NiO nanopowder, which could be due to the formation of p-n heterojunction in the NiO/GO nanocomposites. In particular, the p-type NiO/n-type GO nanocomposites with 65% GO showed the best catalytic activity. Almost 97% of the initial MB dyes were decomposed by the photocatalyst in 50 min. The enhancement of photocatalytic activity can be attributed to the high separation efficiency of photogenerated electrons and holes resulting from the interaction between NiO and GO. Further, we are discussing the effect of different reaction parameters on the photocatalytic activity of the nanocomposite.