This is an analysis of the relations between the Malayan Communist Party and the Indonesian Communist Party in several areas. It will begin with a discussion of the mutual support between the PKI leaders and the Kesatuan Melayu Muda prior to the declaration of Emergency in 1948, followed by an examination of their cooperation immediately after World War II. The second part will look at the activities of the MCP members in Indonesia up to the establishment of the Representative Office of the Malayan National Liberation League in Jakarta. There will be an account of the overt activities of the Representative Office and its covert activities after its closure. The article will also ascertain the actual relations between the two based on a close examination of the official documents of the two parties.