Autotoxicity stress is the principal factor in peach replant problem. Benzoic acid (BA) is known as a critical autotoxin in replant problem, and causes an obvious inhibitory effect on peach growth. Small heat shock proteins (sHSPs) have been reported to play pivotal roles in a variety of physiological and biological processes in various plants. Nevertheless, little is known about the functions and the underlying physiological mechanisms of sHSPs under autotoxicity stress. Here, we identified PpHSP20-26 of peach (Prunus persica) and deciphered its role in BA stress response. PpHSP20-26 was significantly induced by BA treatment. Overexpression of PpHSP20-26 elevated BA tolerance in Arabidopsis and peach plants, whereas down-regulation of PpHSP20-26 in peach through virus-induced gene silencing enhanced BA sensitivity. Compared to the control, the PpHSP20-26-overexpressing plants exhibited lower contents of reactive oxygen species (ROS) and higher activities of antioxidant enzymes. Furthermore, PpHSP20-26 regulated the transcripts of stress-responsive genes including CAT, SOD, APX, GPX, DHAR, and ABC transporters in overexpressing Arabidopsis and silenced peach plants. Taken together, these data suggest that PpHSP20-26 plays a positive role in peach response to BA stress by, at least partly, regulating ROS metabolism and stress-responsive gene expression. Our findings will be of great importance for further understanding the roles of sHSPs genes in autotoxicity stress, and assist crop breeding in mitigating replant problem.