This study examined the effects of microwave on Sarvak heavy crude oil sample from a reservoir in southwest Iran in a Fischer assay and heated by microwave for 2 min time steps until 14 min total heating time had elapsed. Unlike conventional heating, which caused light carbonic components to escape and raised C20+ components in oil samples, the value of light carbonic components increased under microwave heating. These materials cannot escape the oil sample in microwave heating because the cracked components approach a superheated state, and in this study a large portion of them remained. The sulfur content of heavy oil in microwave heating tends to decrease over time, approaching 16% at 14 min; in contrast, in conventional heating it remains constant. Sulfur is removed from the oil sample as H2S and SO2, predominantly in a gas state, but also as condensate, in increasing amounts over time. Sulfur removal from the heavy crude oil sample is highly important in the upgrading process because of having its high coefficient of microwave absorption. Saturation, Aromatic, Resin and Asphaltene (SARA) components analysis shows changes in the resin and asphaltene components. The amount of asphaltene components begins to decline starting early in the heating process, and approaches its lowest amount at 8 min (26% reduction). Reduction of resin components in microwave heating begins at 10 min and reaches 61% at 14 min. According to Fourier transform infrared (FTIR) spectra results, microwave irradiation caused cracking of large-chain molecules and drove light components from heavy crude sample. These two phenomena are a function of radiation time. The rate of cracking of heavy components was continuously greater than the rate of light components leaving the sample at early time intervals; ultimately, this resulted in an upgraded heavy oil.