This paper presents the implementation of a measurement uncertainty assessment guideline applicable to laboratory assessors. Measurement uncertainty is a relevant subject for all laboratories as well as for accreditation bodies since it consists in an elementary requirement for ISO/IEC 17025 accreditation. Therefore, it is crucial to assure that all technical assessors have an adequate level of knowledge about measurement uncertainty and know how to proper assess it. Researching the literature, it is possible to observe that all measurement uncertainty guidelines are focused on the laboratory perspective, to help them implement GUM's concepts. This work, on the other hand, was focused on the implementation of a new measurement uncertainty guideline intended exclusively to help laboratory assessors improve their knowledge about this subject and better prepare them to carry out laboratory assessments. The guideline was implemented in Rede Metrologica RS (RMRS), a regional accreditation body from southern Brazil. Simultaneously to this measurement uncertainty assessment guideline, it was also prepared a measurement uncertainty check-list to help assessors conduct their laboratory assessments. As a result, an improvement on the level of knowledge about measurement uncertainty was observed among RMRS assessors. The improvement was possible to verify through the application of written exams about measurement uncertainty, before and after the training on the new guideline. Exams showed the improvement of assessors' knowledge, demonstrating the relevance of this innovative work.