The bismuth substituted cobalt ferrite CoBixFe2-xO4 (x = 0.1) were synthesized by co-precipitation procedure. The properties of the samples were controlled by heat treatment through annealing processes at temperatures of 300C, 400C, and 500C. After that, all samples were characterized by XRD, FTIR, and VSM. The high purity fcc inverse spinel with Fd-3 space group is obtained following the Rietveld refinement of XRD. The spectrum analysis in the range 400-600 cm-1 confirms the spinel ferrite structure. The net magnetic moment nB, coercive field HC, and magnetization saturation MS of the co-precipitated bismuth substituted cobalt ferrite samples increase with increasing annealing temperature which attributes to the increase of the anisotropy constant.