Co 0.8 Mn 0.2 Fe 2 O 4 and Co 0.7 Mn 0.3 Fe 2 O 4 nanoparticles were synthesized using coprecipitation route. The samples have been annealed at 800°C and have been subjected to further characterization. The phase has been confirmed at 800°C which was determined using XRD. FESEM with EPMA results confirm that the particles synthesized have sizes ranging between 50-70 nm and the composition. From the room temperature magnetic studies, it is seen that Co 0.7 Mn 0.3 Fe 2 O 4 has less saturation magnetization than Co 0.8 Mn 0.2 Fe 2 O 4 and vice versa for coercivity. The magnetic crystalline anisotropy constant has been calculated with the help of "Law of Approach to Saturation". The magnetic crystalline anisotropy constant is found to be greater for Co 0.8 Mn 0.2 Fe 2 O 4 than Co 0.7 Mn 0.3 Fe 2 O 4 . © 2015 AIP Publishing LLC.