This research describes the implementation of authentic assessment of the 2013 curriculum in thematic learning. The study was conducted using descriptive qualitative research, analyzed data through the Miles and Huberman models, then tested the validity of the data through source triangulation and member check. The determination of subjects uses purposive sampling techniques consisting of IIA grade teachers, student criteria based on grades 2, 11 and 21, and principals. The results showed that IIA class teachers applied authentic assessments in a thorough and sustainable manner until class increase, teacher-given assignments related to real-life students, assessments conducted by teachers based on minimum completed criteria. Teachers conduct attitude assessments through observation techniques using journals, teachers also use self-assessment and between friends. Knowledge assessment using written, assignment and oral test techniques with various forms of questions such as multiple selection and stuffing. In assessing teacher skills using performance techniques that are products and practices and using portfolio assessments, by conducting authentic assessments, teachers gather information about student learning achievement, it is also useful for teachers to evaluate learning that suits students' needs and improves the quality of teachers and schools in terms of learning.