One of the Information and Communication Technology (ICT) developments used in the learning process is the Intelligent Tutoring System (ITS), and gamification can overcome boredom, lack of interest or motivation, and monotony when using the ITS. In this study, the application of ITS equipped with Gamification is called ITS + G. Currently, several studies have built the ITS + G. However, there has not been a Systematic Literature Review (SLR) that synthesizes the characteristics of the ITS and Gamification combination. Several previous SLRs have been carried out and discussed the ITS only and several other SLRs discussed gamification only. Therefore, this SLR focused on the characteristics of ITS and gamification as a unit. This study succeeded in synthesizing that ITS + G has the potential to be applied to both STEM and non-STEM subjects. Three main game elements are mostly used in ITS + G: levels, points, and progress bars, which are supported for several reasons. Several techniques that have been used to measure the success of ITS + G are synthesized. Several positive impacts of ITS + G are revealed. Some negative impacts that need to be considered and studied in future research are also noticed. The results of this study could be the basis for ITS + G research in the future and increase the repertoire of knowledge related to ITS and Gamification.