ObjectiveTo identify the effects of transition to siblinghood (TTS) on the firstborn children’s emotions and behaviors, and to define the time of TTS.MethodsCBM, VIP, CNKI, WanFang Data, PubMed, Web of Science and EBSCO were electronically searched to collect studies on the emotional and behavioral characteristics of firstborn children in TTS from inception to December 31st, 2019. Two reviewers independently screened literature, extracted data and assessed the risk bias of included studies. Then, qualitative methods were used to analyze the studies.ResultsA total of 13 studies involving 980 children were included. 12 behavioral related studies explored self-behavior of the firstborn children during TTS, 3 studies focused on the interaction behavior between the firstborn children and their parents, the firstborn children and the second children. The systematic reviews found that TTS showed both positive and negative effects on the behavioral characteristics of firstborn children, primarily the negative effects. Firstborn children’s anxiety, confrontation and attachment showed 3 different patterns over time, respectively. Two studies showed the increase of negative emotions of firstborn children during TTS. The time range of TTS was mainly concentrated in the third trimester to 12 months after the birth of the second child.ConclusionsThe current evidence shows that TTS primarily increases the negative emotions and behaviors of firstborn children, and the behaviors of firstborn children changes over time. Due to limited quality and quantity of the included studies, more high quality studies are required to verify above conclusions.