Influence of the heat treatment, following a wet chemical process, has been examined on the sizes of the obtained particles of MnFe₂O₄. X-ray diffraction, magnetization and Mössbauer measurements have been used. The average sizes of the obtained particles are in the range of ∼ 100 Å–300Å with the upper size limit being ∼ 450 Å and more. The average size as well as size distribution is strongly influenced by the nature of the heat treatment followed for preparation of the sample. Prolonged hydrothermal heating resulted in larger average size than did dry heating at 400°C of the precipitate obtained from the initial wet process. Further dry heating following hydrothermal treatment did not lead to any major growth. Chemical nature of the starting materials also affects the sizes.