The forced convective heat transfer (FCHT) properties of nanofluids, made of Fe 3 O 4 nanomaterials and deionized water, are firstly measured by a self-made forced convective heat transfer apparatus. The nanofluid flows through a horizontal copper tube in the transition region with Reynolds numbers in the range of 2500-5000. Some parameters including Reynolds number, axial distance, and mass concentration are also investigated. The preliminary results are firstly presented that the heat transfer coefficients of Fe 3 O 4 nanofluids systematically decrease with increasing concentration of nanoparticles under transition region which contradicts the initial expectation.