To estimate specific power losses (SPL) of bulky magnetic hyperthermia heating mediators, a hysteresis loop measurement system in alternating magnetic field at a constant temperature was fabricated. Magnetic properties of a rectangular sample of La-Sr-Mn-Cu perovskite (LSMC) in a temperature range of 20～46°C were estimated from induced electromotive force which arose in a single turn pickup coil located at the center of exiting coil (1 MHz, 3 kA/m-rms). Complex permeability μ' and μ", coercive force H_c, and SPL of the LSMC decreased with increasing the temperature. Phase delay δ of magnetic flux density of the LSMC from the applied magnetic field were almost the same among measured temperature range.