This is a descriptive qualitative research. That aims to know where and what kind of mistakes done by the students in completing word problem about ratio and the factors which lead the students conduct mistakes and alternative learning which is used to solve that problem.

After analyzing the students’ work result, three students were selected to become research subject. Based of selection criteria is the number and various mistakes and his fluency in verbal comunication.

The research findings show that the mistakes which were in step of understanding problem: determined what is known and wrote done what is asked incorrectly, planning finalization: wrote dawn mathematical model incorrectly and  mistakes in determine the shape of ratio, appliying finalization plans: wrote the formula incorrectly and mistakes in counting, and rechecking. Kinds of mistakes is: factual, conseptual, principle and operation mistakes.

Meanwhile the factor which caused the students conducting mistakes were: do not have adequate cognitive competence to understand how to change the fraction to percetage, forgot to apply the formula of turned up ratio.

Based on the characteristic of mistakes factors which were committed by the students, the characteristic of problem based learning is one of the effective way to teach it.