Objective：To investigate the expression of high mobility group protein 1（HMGB1） in children with anaphylactoid purpura and its clinical significance. Methods：Expression of serum HMGB1 in 183 children with anaphylactoid purpura was detected by ELISA. HMGB1 mRNA relative expression was detected by real-time PCR. Forty healthy children were enrolled as control group. Results：Serum HMGB1 concentration was higher in anaphylactoid purpura group than in control group（t=7.43，P=0.000） during disease period and after recovery（t=34.257，P=0.000）. HMGB1 mRNA in peripheral blood increased（t=10.362，P=0.000），and decreased after recovery（t=4.651，P=0.000）. There were differences in HMGB1 protein concentration between different genders（t= 0.032，P=0.974），among different ages（F=0.088，P=0.916） as well as between initial onset and recurrence（t=0.449，P=0.654）. There were significant differences in HMGB1 protein concentration between those with and without kidney injury（t=5.672，P=0.000），joint symptoms（t=3.048，P=0.003），and gastrointestinal symptoms（t=2.050，P=0.042）. HMGB1 mRNA relative expression in peripheral blood was higher in those with kidney damage，arthritis symptoms，gastrointestinal symptoms than in those without kidney injury（t=2.867，P=0.005），arthritis symptoms（t=2.733，P=0.007） and gastrointestinal symptoms（t=2.366，P=0.019）. Conclusion：As a new biological marker，HMGB1 could play an important role in diagnosis and treatment of complications of anaphylactoid purpura.