Mathematical creativity is an important thing to be developed in the mathematics teaching learning process. Some mathematics educator argue that mathematical creativity can be developed by providing the right stimulation and assessment in the learning environment. Varying problems are critical for fostering mathematical creativity. Some researchers state that mathematical creativity is observed when one generates a non-standard solution for a problem. Other research confirms that the teacher's experiences of creative mathematics play is an essential role in self-convincing to introduce creative mathematical activities for development of mathematical creativity. However many of preservice-teachers contend that they generally worked on routine mathematics problems and were rarely confronted with problem solving and open-ended mathematics problems. Therefore in this study, the pre-service teachers were given experience in problem solving and open-ended mathematics problems. The activities included solving problems with varied solutions, presenting and reviewing peer-constructed problems, revising, implementing the problems onto mathematic learning processes at school, re-revising and re-organizing the problems. The aim of the paper is to describe an alternative assessment to foster preservice teacher's mathematical creativity. The subjects of the research are 2 lecturers and 23 preservice teachers at on university in Indonesia, on January - April 2017. The preservice teachers are studying in a Bachelor Degree Program and have not had yet teaching experience. During the lecture activities, pre-service teacher were given a project to develop problem solving and open-ended mathematics problems using an Mathematics Instructional Assessment book developed by the researcher. Subsequently, the compiled project drafts were presented by the group and peer-reviewed by other groups of students, while the lecturer served as facilitator. The revised drafts were then implemented by the group in mathematics learning processes at school. The experiences were used to construct and also to revise open-ended mathematical problems. The preservice teachers di not only construct the problems, they also tried to compile an alternative problem solving. In order to assess pre-service teachers' mathematical creativity competence, an assessment rubric has been developed. It was found that through this approach, the mathematical creativity competences of pre-service teachers increased. In other words, an in-class project such as this could serve as an alternative assessment for Mathematics Instructional Assessment subjects supporting the development of pre-service teachers' mathematical creativity.