Objective To investigate the relationship between peripheral blood platelet-lymphocyte ratio, prognostic nutritional index and prognosis in patients with medulloblastoma (MB) after recurrence and before re-treatment. Methods A retrospective study was conducted on 82 patients with MB admitted from September 2015 to September 2022. The post-recurrence OS rates were compared between high/low neutrophil-lymphocyte ratio (NLR) group, high/low platele-lymphocyte ratio (PLR) group, high/low systemic inflammation index (SII) group, and high/low prognostic nutritional index (PNI) group, and the prognostic factors were analyzed. Results The critical values of NLR, PLR, SII and PNI were 3.1, 311.7, 763.7 and 49.0, respectively. Univariate analysis suggested that high NLR, high PLR, high SII and low PNI were associated with shorter OS rate, and the differences between groups were statistically significant (P<0.05). COX regression analysis suggested that PLR was an independent risk factor and PNI was a protective factor for OS after recurrence (P<0.05). The risk of death in the high PLR group was 3.889 times that of the low PLR group, and the risk of death in the high PNI group was 0.484 times that of the low PNI group. Conclusions Relapse has a significant impact on the prognosis of children with MB. For children with recurrent MB, high PNI was a protective factor, but high PLR is a risk factor for a poor prognosis.