A modified controlled chemical co-precipitation of alkaline aqueous ferrous and ferric salt solution at pH 8 with continuous addition of ammonia solution 25% under a degassed atmosphere was performed to synthesis magnetite (Fe3O4) nanoparticles. Formation of magnetite nanoparticles was conducted by adjusting the ferric to ferrous ions in the ratio of 1:1, 1:2 and 2:1. Further investigation on the surfactant-coated magnetite nanoparticles by using 8% surfactant sodium dodecyl sulphate (SDS) was also studied. The synthesized magnetite nanoparticles were characterized by Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer (XRD). TEM results shows that magnetite nanoparticles which were synthesized with ferric/ferrous ratio 2:1 are in sphere shape and have the smallest particle size distribution range which is about 12-17 nm. The particles size distribution range of coated magnetite was decreased to 11-15 nm after coated with 8% surfactant SDS. XPS results indicated that the produced magnetite nanoparticles consisted of elemental iron and oxygen at 72.76% and 22.27% respectively. The phase and face-centered cubic structure of magnetite nanoparticle was also confirmed by XRD. Magnetite nanoparticle synthesized with ferric to ferrous ratio of 2:1 and coated with 8% surfactant SDS shows the best crystallinity among all samples with particle distribution size range from 11-15 nm.