This study aimed at analyzing the implementation of authentic assessments and constraints faced by junior high schools' teachers in mathematics teaching. A qualitative approach was applied in the study. The data on the implementation of authentic assessments and constraints were obtained from 50 mathematics teachers in several public junior high schools in Malang City, East Java Province-Indonesia, trained by the 2013 curriculum. Documentation, questionnaires, observations, and interviews were used to collect the data. The study results showed that most teachers implemented authentic assessments in mathematics teaching as designed in the learning plan. The obstacles faced by the teachers in the implementation of the authentic assessment included the time limit and accuracy. The efforts made by the teachers varied, but the teachers tried to administer the authentic assessment properly following the demands of the curriculum.