Nanosized MnFe₂O₄ particles were prepared by chemical ultrasonic emulsion method. The as-prepared sample was found to be in amorphous state and showed spin-glass behavior at low temperature. The Curie temperature of the annealed sample is 160 K higher than that of the bulk material, which is thought to be due to finite-size scaling and also may be related to a nonequilibrium cation distribution.