In primary schools of Viet Nam, solving problems on  percentages is a very important bit of knowledge because it not only provides a full range of knowledge of percentages but also a lot of practical applications and has a great effect in the development of thinking for students. However, it is a kind of new and difficult problem, so students often commit errors to solve problems on percentages. A survey of 149 primary school students was done. The students had to answer 7 questions about the problems on percentages. Results show that they suffer some errors such as: misunderstanding kinds of problems, doing wrong calculation, confusing the units of measurements. At the end of the paper, some suggestions in mathematics education are made to teachers to support students avoiding errors in solving problems on percentages.