Background Under-nutrition in less than 5 years aged children is one of the global child health concerns, and has got considerable prevalence and trends among different countries in the world with SSA countries giving relatively more large contribution to the global under-5 undernourished population. Insufficient dietary intake and infectious diseases have been reviewed to as the direct causes of under-5 child under-nutrition, of which the underlying causes are household food insecurity, WASH, and improper nutrition health care provision. Basic causes such as inadequate and sustainable funding, and insufficient monitoring and evaluation are more policy related. Under-nutrition may presents with wasting, stunting, underweight or all of them. Under-5 undernutrition especially the first 1000 days (time from pregnancy to the first two years of life) is much concerned with diseases, mortality and disability as short term effects to the child’s complete well being. And, if the child manages to survive for the later years, he/she will develop with poor physical and cognitive abilities. This will ultimately predispose the undernourished community or country at large into poor economic productivity, with poor population. The final outcome of poverty will again raise the issue of households’ food insecurity bringing the core problem of under-5 under-nutrition into a much more seriousness. Objective The target of this study was to determine the basic causes of under-nutrition among Moshi rural children aged by less than 5 years of age, and evaluate the existing policy issues and key stakeholders for promotion of nutrition-sensitive interventions. Methodology This was a cross sectional qualitative research study done through direct interviews with key stakeholders related with promotion of nutrition among children aged below five years. Stakeholders were chosen according to their importance and influence in nutrition related policy making and implementation. x Results Insufficient and unsustainable Government fund, and insufficient monitoring and evaluation of nutrition related interventions were found to be the outstanding basic causes of under-5 child under-nutrition in Moshi rural, as one of the rural areas of Tanzania. The MoHCDGEC, Parliament, International organizations, NGOs, Initiatives (e.g. SUN), district officials, health care providers, nutritionists, and mothers and children (beneficiaries) were identified as important stakeholders with different levels of influence and importance in nutrition related policy making and implementation. Conclusion Global organizations and initiatives like SUN have raise much more concern in promoting child health primarily by insuring a child with good nutrition status. This is trying to keep a child in a well protected environment physically, mentally and socially plus being free from diseases. Tanzania being among the first countries to adopt the SUN global initiative, has started some positive movements towards promoting nutrition throughout the country, including the rural areas like Moshi rural, by putting DNuO at every district, plus other promising steps in nutrition health services promotion. The government through the MoHCDGEC should allocate sufficient fund to nutrition agenda to make improvements in health care infrastructures so that to increase availability and quality of nutrition health services provision to the under five. Monitoring and evaluation of nutrition related interventions, and creation of national nutrition surveillance and information system will strengthen nutrition services in Moshi rural and Tanzania at large.