Mortality rates associated with other indicators of population health plays an important role in decision making in community health, which has been used extensively. Aging populations in developed and developing countries, with increasing mortality among adults, necessitate the need for better assessment of mortality in these ages. The registration procedure is the most appropriate method that can provide mortality statistics and is consistent with its dynamic nature. However, this approach has two major drawbacks: the lack of full coverage and undetermined amount of coverage. Accordingly, the aim of this study is to evaluate the completeness of adult death registration in Markazi and Booshehr provinces, using the Brass Growth Balance method. Results indicate that Completeness of adult death registration in Markazi province is 87/7 percent. This amount is 99/8 percent for male and 76/5 percent for female. But Completeness of adult death registration in Booshehr province is 80/9 percent.  This amount is 91/3 percent for male in comparison with 70 percent for female. Considering this criterion that if the completeness of death registration is over 70 percent, then the death registration is at an acceptable quality level, death registration in these provinces, particularly for men, has an appropriate completeness.  However, as research results show, mortality registration data for women encounters so many problem the completeness of women death registration percent ratio is 20 less in number than that of men.