Pathogenesis-related proteins (PRs), systemic acquired resistance (SAR) marker genes closely related to plant disease resistance, play an important role in plant defense systems. A PR gene ZaPR4b has been cloned from Zanthoxylum armatum in this study. Sequence analysis showed that ZaPR4b’s ORF is 435 bp in length, encoding 144 amino acid protein and had a Barwin domain, belonged to the class II PR4 family. Bioinformatics analysis showed that ZaPR4b is a stable, hydrophilic secretory protein, which is closely related to PR4b in peach, rubber tree, and cassava. Subcellular localization results showed that ZaPR4 is localized to plasma membrane in tobacco epidermal cells. qPCR results showed that ZaPR4b is highly expressed in the leaves and fruits and slightly expressed in the roots and stem. Furthermore, more, the expression of ZaPR4b was positively correlated with the leaf rust resistance of different resistant varieties. Salicylic acid (SA) induction substantially increased the expression levels of ZaPR4b gene and enhanced its resistance to leaf rust. These findings provide a more definite knowledge on the molecular basis of signal transduction in the response of Z. armatum to leaf rust.