The article aims to describe students' task that concerned to assess students’ problem proving and problem posing on triangle task. The method used is descriptive-explorative research Participants of the research were 24 prospective mathematics teachers at a state university in Surabaya city, Indonesia. All students had to answer three questions. The first question related to problem proving of triangle theorem. The second question related to their perception of the first question, and the last question related to the problem posing task. A Newman analysis is used to analyse the data. Analysis focused on students’ problem proving and students’ problem posing of triangle task. Some results showed that most prospective teachers the most found in the prospective teachers’ answer, mainly 41%. It can be seen at question 1was performed by the highest number of prospective teachers. However, some of the prospective teachers still have a perception question 1 is a problem, because it shows as many as 95% of 24 students choose it. Furthermore, the students have some weaknesses in proving problems, mainly misinformation or ambiguity about problem, it is not category as problem proving. They constructed proof by formal proof with low level of problem difficulty as many as only 38 % of 24 students.