As a social human and God's creature, people interacting with others through human communication(interpersonal communication). Interpersonal communication generally involves two people whose communicateeach other, whether they already knew or never known each other. Berger and Calabresse (in West and Turner,2013: 174) believed it is natural to have doubts about our ability to predict the outcome of initial encounters. Heis also argued that the beginnings of personal relationships are fraught with uncertainties and communicationbecomes the primary method to reduce these uncertainties. On The Job Training Program is a program that wasorganized for the subsidiaries of Hitachi Construction Machinery (HCM) Group that is in some countries suchas Indonesia, Russia, China, Malaysia, etc. Since they start of the program in Japan, the participants especiallyfrom PT. Hitachi Construction Machinery Indonesia feel the differences such as the work climate, culture, and thepersonal character of the Japanese people. These differences make the participants feel the uncertainty. By applyingUncertainty Reduction Theory, this research is aim to examine uncertainties perceived by the participants On TheJob Training Program of PT. Hitachi Construction Machinery Indonesia, especially in their interpersonal communicationactivities with other participants from Japan. In addition, this research aims to examine participantstrategies to reduce these uncertainties.