The facts show that the mathematics achievement of Indonesian students is still very low. One of the causes of this problem is that the learning model used by the teacher is still conventional. This study aims to describe the activities of Mathematics Prospective Teachers (MPT) in completing assignments/projects using the Outdoor Learning Mathematics Project (OLMP). The research subjects were 29 MPT at the Faculty of Teacher Training and Education University of Jember, Indonesia, in August 2022. The type of research was quasi-experimental using one group pretest-posttest design and a one-shot case study. Data were collected using observation sheets, worksheets, learning outcome tests, and questionnaires. Data analysis used descriptive qualitative statistics. From the results of the data analysis, it can be concluded that the OLMP model is effective in increasing the activities of MPT. This can be seen that all groups are very active in carrying out very varied activities during learning activities in the Campus Garden. They can find many mathematical concepts and apply them to complete projects. In addition, with an N-gain score of 0.79, the OLMP model is effective in improving the learning outcomes of MPT. The majority of the subjects (97.59%) have a very positive response concerning the application of the OLMP teaching model. In the future, further research needs to be carried out using more subjects from various fields of science, and in many places. It is hoped that MPT can be skilled in guiding students using the OLMP model when they are already teachers at school.