L-asparaginase (L-ASNase) is an enzyme used most effectively in the treatment of acute lymphoblastic leukemia (ALL) for more than 30 years. It catalyzes the hydrolysis of amino acid l-asparagine to aspartic acid and ammonia, which leads to cell death. Clinical trials have been conducted using L-ASNase in combination with other drugs and radiotherapy, which have led to great success in the treatment of ALL. Treatments consist of induction therapy and central nervous system therapy. The achievement of complete remission in patients is associated with a few side-effects of using L-asparaginase, including pancreatitis, coagulation abnormalities and allergic reactions. Sometimes tumor cells may develop resistance to L-ASNase. To overcome these difficulties, the drug is modified by pegylation or immobilization, and also treatment protocols can be modified to increase the efficiency of the drug.