The use of educational game in teaching and learning is increasingly relevant trend. Interface and usability are common elements in games development and important elements for evaluation purposes. This study is aiming to develop a methodology for heuristics based formative usability evaluation that can be used to evaluate interface of educational game. The methodology includes set of evaluation questions for different types of evaluators which are expected to optimize the use of resources regarding the online evaluation tool. The methodology is intended for the evaluation of educational games during its development process.