Recently, polymer phase behavior got much attention both in scientific research and industrial applications. Phase separation plays a vital role during practical applications of polymer mixture as the properties depend on its dynamics and structures. Researchers put intense interest to analyze phase separation of immiscible polymer blends and observed that various factors such as temperature, molecular weight, substrate and film thickness influence polymer phase separation process. Among them, film thickness dependence got immense attraction now a days. Film thickness dependence of phase separation of binary polymer mixture coupled with various analytical techniques, is discussed in Film thickness, phase separation, microscopic analysis, AFM, SEM, XPS, TEM this review.