The magnetic properties of nano-crystallite cobalt lanthanum ferrite (CoLa(x)Fe(2-x) O(4)) with varied quantities of lanthanum (x = 0, 0.1, 0.15, 0.2, 0.25, 0.3) prepared by co-precipitation method have been studied by vibrating sample magnetometer (VSM) and LCR meter. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the size, structure, and morphology of the ferrite samples. The average crystallite size varied from 17.83 nm to 49.99 nm. All the samples, although, in nano range, show significant hysteresis. The saturation magnetization (M(s)) values decreased from 60.57 emu/g to 30.15 emu/g. The remanence (M(R)) fell from 10.85 emu/g to 6.39 emu/g. Doping with lanthanum La(3+) ions modulates significantly the magnetic properties of cobalt spinel ferrites without sacrificing the ferromagnetic character.2725155