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Cysteine-rich secretory proteins (C), antigen 5 (A), and pathogenesis-related 1 proteins (P) comprise widespread CAP superfamily proteins, which have been proven to be novel virulence factors of mammalian pathogenic fungi and some plant pathogens. Despite this, the identification and function of CAP proteins in more species of plant pathogens still need to be studied. This work presents the identification and functional analysis of CAP superfamily proteins from <i>Puccinia striiformis</i> f. sp. <i>tritici</i> (<i>Pst</i>), an important fungal pathogen that causes wheat stripe rust on wheat worldwide. A total of six <i>CAP</i> genes were identified in the <i>Pst</i> genome, designated as <i>PsCAP1</i>–<i>PsCAP6</i>. Five PsCAP proteins, including PsCAP1, PsCAP2, PsCAP3, PsCAP4, and PsCAP5, have N-terminal signal peptides secreted with the yeast signal sequence trap assay. Single-nucleotide polymorphism (SNP) analysis indicated that they showed a low level of intraspecies polymorphism. The expression abundance of <i>PsCAP</i> genes at different <i>Pst</i> infection stages was detected by RT-qPCR, and most of them were highly expressed during <i>Pst</i> infection on wheat and also <i>Pst</i> sexual reproduction on barberry (<i>Berberis shensiana</i>). Noticeably, the silencing of these six <i>PsCAP</i> genes by BSMV-mediated HIGS indicated that <i>PsCAP1</i>, <i>PsCAP4</i>, and <i>PsCAP5</i> contribute significantly to <i>Pst</i> infection in wheat. These results indicate that PsCAP proteins may act as virulence factors during <i>Pst</i> infection, which also provides insights into <i>Pst</i> pathogenicity.