A cDNA clone of a soybean gene encoding a proline-rich protein (PRP) was characterized and designated SbPRP (Soybean Proline-rich Protein). The SbPRP protein is a putative bimodular protein of 126 amino acids with a proline-rich domain and a hydrophobic cysteine-rich domain plus a signal peptide at the N terminal. Southern analysis indicates the presence of a single copy of the SbPRP gene in the soybean genome. The SbPRP gene expression was investigated and the results demonstrate that it accumulates in leaves and epicotyls of soybean seedlings, but not in cotyledons, hypocotyls and roots. The SbPRP mRNA was also expressed in response to salicylic acid and virus infection. In addition, the SbPRP gene transcription was regulated by circadian rhythm, salt stress, drought stress and plant hormones. These results indicate that the SbPRP gene might play a role in plant responses to multiple internal and external factors.