ParA1 is an elicitin secreted by pathogenic Phytophthora species, which can induce defense reactions in plants. In the present study, we report the identification and functional characterization of two mutant proteins generated from ParA1. Val13Ala (V13 A) and Asp25Ser (N25S) were obtained with site directed mutagenesis and recruited to determine their biological activities. Empirical data indicated that V13 A suffered significant loss of functions including elicitation of hypersensitive response (HR) and resistance to bacterial and TMV infections in plants; while N25S behaved the same as ParA1 proteins in all the biological activity tests. The results indicated that residue 13 (Val) was a novel activity-determining residue site in ParA1, whereas residue 25 (Asp) was not as essential as residue 13 (Val) in ParA1.