ABSTRACT: Electronic structure calculation of bulk and monolayer MoS2 has been performed using plane wave pseudopotential method based on density functional theory. The indirect band gap in the bulk MoS2 was found to be 0.9 eV, whereas in the monolayer-MoS2 the band gap of 1.57 eV was found to be direct one. The calculated physical parameters of monolayer MoS2 are found to be very close to the bulk MoS2 and compare well with available experimental and other theoretical results. The calculated density of states (DOS) may help explain this change in the nature of band gap in bulk and in monolayer MoS2. A further variation in band gap has been observed in MoS2 monolayer on applying biaxial strain.