Objective: To evaluate the clinical efficacy and adverse events of recombinant human interleukin-11(rhIL-11) in the prevention of thrombocytopenia induced by craniospinal irradiation. Methods: In this randomized control study, 100 patients were randomly divided into A (rhIL-11 group, n=50) and B groups (control group, n=50). In the A group, subcutaneous injection of rhIL-11 was delivered at a dose of 50 μg/kg/d, once daily when the platelet count was< 100×10⁹/L during radiotherapy or decreased by> 50% compared with the baseline level. The administration of rhIL-11 was terminated when the platelet count was ≥ 200×10⁹/L. In the B group, the same protocol was conducted when the platelet count was< 50×10⁹/L and terminated until the platelet count was ≥ 100×10⁹/L. The clinical efficacy was assessed in 92 patients. Subcutaneous injection of rhIL-11 could significantly elevate the minimal platelet count during craniospinal irradiation (P<0.01), considerably shorten the duration of thrombocytopenia (P<0.01) and effectively shorten the duration of radiotherapy (P<0.01). Main adverse events included mild pain at the injection site, sclerosis, redness and fatigue, etc. Conclusions Injection of rhIL-11 can significantly enhance the platelet count, effectively reduce the incidence of thrombocytopenia throughout craniospinal irradiation, guarantee the success of radiotherapy and yield mild adverse events.