Phosphofructokinase-2 was purified to homogeneity from chicken livers by homogenization, polyethylene glycol fractionation and column chromatography on DEAE-Sephadex A-50 and Blue-Sepharose 4B. Some properties of the enzyme were as follows: (i) The saturation curve of the enzyme for fructose 6-phosphate showed hyperbolic and the Km of fructose 6-phosphate was affected by inorganic phosphate while Vmax was not; (ii) the binding of ATP to the enzyme was of negative cooperativity with a Hill coefficient of 0.56; (iii) the activity of the enzyme was completely lost in the presence of EDTA. The enzyme was activated by Mg2+ at low concentrations, but inhibited by Mg2+ at high concentrations; (iv) the enzyme was stable below 30 degrees C and easily lost its activity when the temperature was above 40 degrees C; (v) the activity of the enzyme was stable at the range of pH 7-9, increased at pH 9.0-9.5 and decreased when pH was over 9.5; (vi) the enzyme was sensitive to trypsin and ATP protected the enzyme against the proteolysis of trypsin.