In this paper, we have proposed a fast inter-processor communication interface (IPC) for a dual-core Java application processor. The dual-core Java application processor is a SoC composed of a RISC core and a double-issued Java bytecode execution core. The proposed fast IPC mechanism provides Java system software a high-level way to invoke a host processor service routine from Java source code. The proposed IPC has much lower overhead than that of the standard Java Native Interface (JNI). Unlike other fast native call interface designed for VM interpreter, the proposed IPC mechanism is exclusively designed for the communication between two physical hardwired processor cores. Based on the experimental results, the proposed mechanism is very promising for embedded Java runtime environment.