Mannan-binding lectin-associated serine protease-2 (MASP-2) is an essential component of the lectin pathway of complement activation. Its serum concentrations show a wide interindividual variability. The aim of our study was to determine if serum concentrations of MASP-2 differ between children with Acute lymphoblastic leukemia (ALL) and healthy age-matched controls. This study included 48 individuals: 37 children with Acute lymphoblastic leukemia (ALL) and 11 healthy age-matched controls. Serum levels of MASP-2 were evaluated by ELISA. The results showed that children with Acute lymphoblastic leukemia had higher median MASP-2 serum concentrations (509 ± 351.8 ng/mL) compared to healthy age-matched controls (284 ± 35.4 ng/mL), (p<0.05). This indicates the Acute lymphoblastic leukaemia associated with high levels of MASP-2 and suggests the possibility to use MASP-2 as diagnostic biomarker for Acute lymphoblastic leukaemia.