The effect of a thin Ta layer inserted between Pt and CoFeB layers on perpendicular magnetic anisotropy (PMA) with MgO barrier layer has been studied. The crystallinity was studied by performing high-resolution x-ray diffraction (HR-XRD) technique. While the crystal peak of Pt is observed in all sample stack that is oriented as (111) face-centered cubic crystal structure, a very weak and broad alpha-Ta (110) peak is observed when Ta layer thickness is above 0.8 nm. Magneto-optical Kerr effect (MOKE) measurements show that the PMA could be enhanced by inserting Ta layer between Pt and CoFeB layer. The magnetically dead layer thickness (t(dead)) and the interfacial anisotropy energy density (K-i) of the various Ta-inserted layer thickness were found as 0.135 nm; 0.75 erg/cm(2), 0.141 nm; 1.02 erg/cm(2), 0.187 nm; 1.15 erg/cm(2), for t(Ta) = 0.0, 0.5, and 1.0 nm, respectively. Both t(dead) and K-i increase with Ta-inserted layer thickness in Pt/Ta(t)/CoFeB/MgO multilayer film stack. The sources of interfacial magnetic anisotropy can be hybridization, crystallinity properties, and/or B/Ta diffusion effect at the interfaces in Pt/Ta(t)/CoFeB/MgO multilayer film stack.