Interface of Co/Si bilayer system on Si (100) substrate have been studied using in‐situ magneto optical Kerr effect (MOKE). Interface selectivity of the technique was achieved by performing measurements during deposition of nonmagnetic Si layer on 30 nm thick Co film. At around 29.5 nm thick Si film limits laser penetration upto Co‐Si interface and hysteresis loops were obtained from interface. Sample was also annealed in‐situ in order to increase interface contribution due to the intermixing at the interface. In the present work, we have demonstrated that the in‐situ magneto‐optical Kerr effect technique can be used for evaluation of ferromagnetism around the buried interfaces.