The phase transitions in LiNH4SO4 (LAS) were studied below and above room temperature by means of several techniques: modulated differential scanning calorimetry (MDSC), capacitance and ac thermal measurements. Our results show four distinct phases transitions at 460, 285, 225 and 28 K on cooling runs. The phase transitions at 460 and 285 K are of first order. The 225 K phase transitions is reported for the first time. The capacitance results show a strong hysteretic behavior in the 225 K transition on successive heating and cooling cycles attributed to the field effect on the polar ordering.