We report the preparation of mono phasic Zr-substituted magnetite (Zr_xFe_3-xO₄; 0≤x≤1) nano particles by wet chemical route. Such are portislacking in the literature. Rietveld refinement of the X-ray diffraction (XRD) data suggests continuous decrease in the lattice parameter with increased Zr-substitutions. From TEM analysis, the size of the as synthesized particles was found to be in the range of 5– 20 nm. The differentials canning calorimetry (DSC)curves for the samples with different amount of substitutions displayed considerable differences in their behaviors. The room temperature specific magnetization at 2T has been found to decrease from 50(x=0.2) to 41A m²/kg (x=1.0) with increased Zr-substitution. From XRD and magnetic behaviour analysis we could suggest that due to occupation of Zr⁴⁺ ions at tetrahedral and octahedral voids of Fe₃O₄, the amount of Fe²⁺ was more at octahedral site for x≤0.4 and at tetrahedral site for x>0.4 respectively. The ferrofluids prepared from these magnetic nano particles possessed good heating ability and Specific Absorption Rate (SAR) values suitable for bio applications.