Ferrofluid (magnetite/Fe3O4 magnetic fluid) is colloidal suspension containing Fe3O4 nanoparticles dispersed in a liquid carrier. In this work, Fe3O4 particles in the fluid have been prepared by a simple co-precipitation route. The nano-structural behaviors such as phase purity and crystal structure of magnetite particles in ferrofluid were studied by means of X-ray diffractometry (XRD). Meanwhile, the form and structure factors were investigated by small-angle neutron scattering (SANS) spectrometer. The XRD pattern confirmed a single phase of spinel cubic Fe3O4 structure. Further XRD data analysis revealed that the magnetite has a lattice parameter of 8.38 Å. The SANS data was fitted by applying a lognormal spherical calculation as a form factor and a mass fractal model as a structure factor. It showed that the magnetite ferrofluid has primary particles of 7.6 nm in diameter with fractal dimension of 1.2, which can be associated with chainlike structure. The chain-like structured Fe3O4 ferrofluid based on local natural iron sand in this work opens new opportunities to be applied for novel prospective applications.