The object of this study is multicomponent heterogeneous liquid-liquid system with n-amyl acetate synthesis reaction. New experimental data on solubility, liquid-liquid equilibrium (LLE) and critical compositions for acetic acid – n-amyl alcohol – n-amyl acetate – water at 303.15 K and atmospheric pressure are presented. Solubility and critical states were investigated by “cloud-point technique” and pale opalescence blue methods accordingly. LLE compositions were determined by gas chromatography and correlated by NRTL model. Results calculated using NRTL modeling are in sufficient agreement with experimental data. Standard deviations for binary, ternary subsystems do not exceed 0.45% and for quaternary system investigated – 0.53%.