Cobalt ferrite nanoparticles were synthetized by co-precipitation technique from nitrate precursors. X-ray diffraction confirms the formation of the spinel ferrite. SEM and HRTEM micrographs corroborate the formation of agglomerated nanoparticles of 8-35 nm size range with 21.7 nm average size. The broad size distribution and considerable agglomeration of the particles hamper the superparamagnetic state of the sample, provoking a weak coercivity at room temperature. In contrast to several other magnetic nanostructures, the ZFC-FC curves of cobalt-ferrite nanoparticles revealed an unusually large magnetostriction, evidenced by larger values of magnetization in their ZFC curves than the FC curves in the measured temperature range 20-375 K. The behavior could be reversed on applying high magnetic fields. However, the maximum of ZFC curve reduces on increasing the applied magnetic field.