This study investigates the physical properties of an iron-nickel based metallic glass alloy (Fe₃₉Ni₃₉Mo₄Si₆B₁₂) which was initially fabricated in an amorphous state using the Planar Flow Casting Method, after being subjected to heat treatment at 500 ^oC for periods of 1, 5, and 30 minutes. The resulting structural and physical changes, particularly the transition from amorphous to crystalline, were analyzed using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Fluorescence (XRF), and Vickers hardness testing. Both XRD and SEM analyses consistently showed that crystallization and associated phase transformations become more evident as the heat treatment duration increases, a process visually documented by the SEM images showing the amorphous-to-crystalline sequence. Furthermore, the Vickers hardness measurements revealed a clear increase in hardness resulting from the heat treatments, which was measured for each step of heat treatments. The presence of the constituent elements was confirmed via XRD and XRF analyses. Based on these experimental observations, it is concluded that the Fe₃₉Ni₃₉Mo₄Si₆B₁₂ metallic glass alloy is a promising candidate for applications in magnetic sensors and transmitters.