This study represents an experimental investigation of the effect of utilizing hybrid nanofluid (Al2O3-TiO2/water) and its flow rates on heat transfer coefficient and thermal performance of the double-pipe heat exchanger measuring 1m in length of 9.5 mm inner diameter and 19 mm outer diameter made up the experimental setup. The nanofluid that was utilized as a coolant is TiO2 (20 nm) and Al2O3 (50 nm) nanoparticles in pure water as a base fluid and a mixing ratio of 50% of both. Different volume concentrations (0.1, 0.3, and 0.5%) and flow rates of (3, 4 and 5) L/min were tested at inlet temperature of 20 ℃ and Reynolds number ranging from (7066–11793). The obtained results showed that the maximum increase in Nusselt number was 12.16% and 28.4% with volume concentrations of 0.1% and 0.5%, respectively, when compared to those of pure water. Also, the maximum thermal performance effectiveness was 33.36%, achieved at volume concentration of 0.5% with a volume flow rate of 5 L/min. Thus, the heat transfer performance of the nanofluid has been significantly improved.