The article reviews the complex functions of serine/arginine-rich (SR) proteins in pre-mRNA splicing. SR proteins play multiple roles, including regulating alternative splicing and constitutive splicing. They have modular structures, with an N-terminal RNA-binding domain and a C-terminal RS domain. The RNA-binding domains can be exchanged between SR proteins, and the RS domains function as protein interaction domains. Recent studies have revealed that SR proteins recognize a wide range of RNA sequences and interact with various splicing factors, such as U2AF and U1-70K. The RS domains are phosphorylated, and this phosphorylation influences their subcellular localization and protein interactions. SR proteins are involved in regulated 3' and 5' splice site selection, as well as constitutive splicing. They can promote the recognition of alternative splice sites and participate in the pairing of 5' and 3' splice sites. The article discusses the exon-dependent and exon-independent functions of SR proteins, highlighting that multiple SR protein molecules participate in the splicing of each intron. The findings suggest that different SR protein functions may be performed by distinct molecules, with some functions requiring multiple SR proteins. The review also addresses the structural organization of SR proteins and the role of their RS domains in splicing. Overall, the article provides a comprehensive overview of the recent advances in understanding SR protein functions and their mechanisms in pre-mRNA splicing.The article reviews the complex functions of serine/arginine-rich (SR) proteins in pre-mRNA splicing. SR proteins play multiple roles, including regulating alternative splicing and constitutive splicing. They have modular structures, with an N-terminal RNA-binding domain and a C-terminal RS domain. The RNA-binding domains can be exchanged between SR proteins, and the RS domains function as protein interaction domains. Recent studies have revealed that SR proteins recognize a wide range of RNA sequences and interact with various splicing factors, such as U2AF and U1-70K. The RS domains are phosphorylated, and this phosphorylation influences their subcellular localization and protein interactions. SR proteins are involved in regulated 3' and 5' splice site selection, as well as constitutive splicing. They can promote the recognition of alternative splice sites and participate in the pairing of 5' and 3' splice sites. The article discusses the exon-dependent and exon-independent functions of SR proteins, highlighting that multiple SR protein molecules participate in the splicing of each intron. The findings suggest that different SR protein functions may be performed by distinct molecules, with some functions requiring multiple SR proteins. The review also addresses the structural organization of SR proteins and the role of their RS domains in splicing. Overall, the article provides a comprehensive overview of the recent advances in understanding SR protein functions and their mechanisms in pre-mRNA splicing.