The effects of protein concentration, temperature, heating time, salt ions and their concentration, and pH on the antioxidant activities of proteins including peach kernel protein isolates(PKPI), soy protein isolates (SPI), whey protein isolates (WPI), casein(CA) were investigated by deterrnining their DPPH free radical scavenging capacities, and taking 6-Hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) as the control. The results showed that at the concentrations of 0.05～2.00 g/100 mL, the antioxidant activities of these proteins increased with the increase in the concentration; Temperature had different effects on proteins’ antioxidant capacities with PKPI, WPI, CA, and SPI obtaining the best antioxidant activities at 40, 40, 30 and 70 ℃, respectively. Little effects of heating time were observed on SPI, CA and PKPI antioxidant activities at their optimal temperatures, respectively, while increasing heating time somehow improved the antioxidant activity of WPI at 40 ℃. 0～10 mmol/L, NaCl and CaCl₂ had less impact on the antioxidant activities of CA and SPI than that of WPI. Moreover, the effect of CaCl₂ on the decreased antioxidant capability of WPI was bigger than NaCl. NaCl had little influence on the antioxidant capacity of PKPI. However, increasing CaCl₂ reduced PKPI’s antioxidant activity. These proteins’ antioxidant activities were greatly influenced by pH. And at pH 2.0, their antioxidant capacities were higher than those at pH 8.0.