In this research, faujasite-type zeolite and iron oxide mixed catalyst were successfully synthesized to decrease the viscosity of heavy oil in an aquathermolysis reaction. Faujasite-type zeolite was synthesized using a microwaves-assisted thermal reaction and ultrasonic waves at different aging times, varied at 0, 7, 21 and 28 days. The iron oxide was synthesized by co-precipitation at low temperature. The XRD results showed that zeolite crystallization occurred after 5 days of aging time and achieved uniform crystallinity after 7, 14 and 28 days. The zeolite samples with 7 days of aging time had the smallest particle size (82.1 nm) and the largest specific surface area (304 m2 g−1). The FTIR spectrum of the heavy oil indicated a catalyst effect on the breakdown of the C–O, C–C and C–S hydrocarbon chains as well as an increase in transmittance peak in saturated C–H and C–H aromatic bonds. The catalytic test through the aquathermolysis showed that the catalyst with the highest efficiency (81.5%) was found among the zeolite samples with 7 days of aging time (FAU-7). Based on these results, the synthesized catalyst can be used to reduce the viscosity of heavy oils.