Magnetic nanofluids are an outstanding candidate for biomedicine research. This is because their magnetic properties play a significant role in evaluating the effectiveness of clinical applications in biomedicine. Besides, that is influenced by many factors, the most important of which is particle size. In this article, we present a simulation study to assess the effect of particle size on the magnetic properties of magnetic fluids which contain the magnetite (Fe3O4) nanoparticles ensemble with their physical size variation between 2 nm and 20 nm (Critical size range for biomedical applications). These results show that the magnetic properties of microfluidics strongly depend on the size of the component nanoparticles. In addition, they are also compared with experimental results reported by other authors recently, showing good agreement and providing some valuable predictions.