Abstract: A JAVA program language compile-on-demand service system and method for accelerating a processing speed of a JAVA program in a data processing system having a relatively low performance is provided. The JAVA COD service system compiles a JAVA class file to be executed in a data processing system into a pattern which can be executed more speedily on the data processing system, and then transmits the compiled result, upon a request of the data processing system connected via a network in order to execute the JAVA program at a relatively faster speed. The system includes JAVA program providing servers, data processing systems, and a compile-on-demand server for receiving a service request, downloading a requested JAVA class file, compiling the downloaded JAVA class file, and transmitting the compiled result.