Objective To compare the differences of immunological characteristics between newborn and adults, we performed high-throughput sequencing to reveal the diversity of umbilical cord blood and adult peripheral blood at both T-cell receptor beta chain (TRB) and immunoglobulin heavy chain (IGH) levels. Study design High-throughput sequencing was performed to analyze the expression of TRB-CDR3 and IGH-CDR3 in circulating T and B cells isolated from 20 healthy adults, 56 pregnant women, and 40 newborns. Results Our results revealed different immunological characteristics between newborn and adults, such as distinctive complementarity determining region 3 (CDR3) lengths, usage bias of variable and joining segments, randomnucleotide addition, a large number of unique CDR3 peptides, and a greater repertoire diversity. Moreover, each newborn had a distinctive TRB-/IGH-CDR3 repertoire that was independent of the maternal immune status. Conclusions This study presents comprehensive, unrestricted profiles of the TRB/IGH-CDR3 repertoire of newborns, pregnant women, and healthy adults at a sequence-level resolution. Our data may contribute to a better understanding of the immune system of newborns and benefit the efficient application of umbilical cord blood transplantation in future.