Mn-Ferrite nanoparticles were prepared using citrate auto combustion method. The prepared sample was characterized by X-ray diffraction (XRD), HRTEM and BET to measure the particle diameter and the surface area of the prepared sample. The data of XRD clarified that the sample was formed in single phase spinel structure without any extra peaks indicating non-existence of any secondary phase. The HRTEM micrograph indicated that the particles were in an agglomerated state due to the absence of surfactant and high magnetic properties of Mn-Ferrite nanoparticles. The mechanical properties were measured at different ratios of nano-Ferrite to concrete. The obtained values of mercury intrusion porosimetry (MIP) indicated that the addition of Mn-Ferrite nanoparticles increased the compressive strength and decreased the total intrusion volume. This was due to the rapid consuming of Ca(OH)2 which was formed during hydration of Portland cement especially at early ages due to the high reactivity of MnFe2O4 nanoparticles. Moreover, MnFe2O4 nanoparticles recovered the particle packing density of the blended cement, leading to a reduced volume of pores in the cement paste.