L-Asparaginase (L-asp), the unconjugated form of polyethylene glycol-conjugated L-asparaginase (PEG-asp), regulates T cell stimulation, antibody production, and lysosomal protease activity to mediate PEG-asp-related anaphylaxis. This study aimed to investigate the relation of L-asp activity and anti-L-asp antibody with anaphylaxis risk and non-anaphylaxis adverse reaction risk in childhood acute lymphoblastic leukemia (ALL) patients who underwent PEG-asp contained therapy.In total, 170 childhood ALL patients underwent PEG-asp-contained treatment and their L-asp activity and anti-L-asp antibody were detected on the 7th day after treatment initiation.There were 27 (15.9%) patients who had PEG-asp-related adverse reaction: 17 (10.0%) patients experienced PEG-asp-related anaphylaxis and 14 (8.2%) patients experienced PEG- asp-related non-anaphylaxis adverse reaction. Moreover, L-asp activity was negatively related to anti-L-asp antibody in childhood ALL patients (P<0.001). Elevated L-asp activity was associated with the absence of PEG-asp-related anaphylaxis (P<0.001), PEG-asp-related non-anaphylaxis adverse reaction (P=0.004), and PEG-asp-related adverse reaction (P<0.001). However, the anti- L-asp antibody displayed opposite trend similar to L-asp activity. Receiver operating characteristic (ROC) curve analyses exhibited L-asp activity and anti-L-asp antibody exhibited superior predictive values in estimating PEG-asp-related anaphylaxis risk with area under curve (AUC) of 0.955 and 0.905, respectively compared to PEG-asp-related non-anaphylaxis adverse reaction risk with AUC of 0.730 and 0.675, respectively. Besides, patients with de novo disease, higher risk stratification, and allergic history showed trends linked with PEG-asp-related anaphylaxis risk.The monitoring of L-asp activity and anti-L-asp antibody maybe useful for early estimation and prevention of PEG-asp-related anaphylaxis in childhood ALL management.