Tanzania has made great progress in reducing diarrhea mortality in under- five children. We examined factors associated with the decline and projected the impact of scaling up interventions or reducing risk factors on diarrhea deaths.We reviewed economic, health, and diarrhea-related policies, reports and programs implemented during 1980 to 2015. We used the Lives Saved Tool to determine the percentage reduction in diarrhea-specific mortality attributable to changes in coverage of the interventions and risk factors, including direct diarrhea-related interventions, nutrition, and water, sanitation and hygiene (WASH). We projected the number of diarrhea deaths that could be prevented in 2030, assuming near universal coverage of different intervention packages.Diarrhea-specific mortality among under-five children in Tanzania declined by 89% from 35.3 deaths per 1000 live births in 1980 to 3.9 deaths per 1000 live births in 2015. Factors associated with diarrhea-specific under-five mortality reduction included oral rehydration solution (ORS) use, changes in stunting prevalence, vitamin A supplementation, rotavirus vaccine, change in wasting prevalence and change in age-appropriate breastfeeding practices. Universal coverage of direct diarrhea, nutrition and WASH interventions has the potential reduce the diarrhea-specific mortality rate by 90%.Scaling up of a few key childhood interventions such as ORS and nutrition, and reducing the prevalence of stunting would address the remaining diarrhea-specific under-five mortality by 2030.