Allograft fibrosis is increasingly detected in graft biopsies as the postoperative period extends, potentially emerging as a pivotal determinant of long-term graft function and graft survival among pediatric recipients. Currently, there is a paucity of noninvasive diagnostic tools capable of identifying allograft fibrosis in pediatric recipients of liver transplants. This study involved 507 pediatric liver transplant patients and developed a novel blood-based diagnostic assay, Pediatric Liver Transplantation-Liver Fibrosis Evaluation (PT-LIFE), to noninvasively distinguish allograft fibrosis using blood samples, clinical data, and biopsy outcomes. The PT-LIFE assay was derived from a matrix of 23 variables and validated in 2 independent cohorts. It integrates 3 biomarkers (LECT2, YKL-40, FBLN3) with an area under the receiver operating characteristic curve of 0.91. In the pooled analysis, a PT-LIFE score lower than 0.12 identified liver allograft fibrosis semiquantitative scores 0 to 2 with a sensitivity of 91.9%, whereas scores above 0.29 indicated liver allograft fibrosis semiquantitative scores 3 to 6, with a specificity of 88.4%. The PT-LIFE assay presents as a promising noninvasive diagnostic tool for the detection of allograft fibrosis in pediatric liver transplant recipients.