The effects of 200 MeV Ag15+ ion irradiation on structural, magnetic and dielectric properties of nanocrystalline Mn-Ca ferrite have been investigated. The specimens characterized using XRD confirmed the formation of cubic spinel structure. The TEM images revealed the spherical morphology consistent with the crystalline diameter. After irradiation by 200 MeV Ag ions, saturation magnetization, coercivity, and blocking temperature were enhanced appreciably which could be attributed to swift heavy ion (SHI) irradiation induced modifications in surface states of the nanoparticles, slight increase in crystallite size and cationic re-distribution. The dielectric measurements revealed that both dielectric constant (epsilon(r)) and the loss tangent (tan delta) disperse normally as a function of frequency of the externally applied electric field. The increase in epsilon(r) and tan delta on irradiation could be attributed to the surface modifications through slight crystal growth and hence the availability of sufficient number of Fe2+/Mn3+ ions particularly at the octahedral site on grain boundaries showing a fair agreement with the magnetization results. (C) 2011 Elsevier B. V. All rights reserved.