This study aimed at investigating the contributions of cooperative unions towards improvement of peasants’ welfare in Magu and Kwimba districts Mwanza region from 1920s – 2000s. The study has two specific objectives: to identify the benefits of cooperative unions in Mwanza region in Kwimba and Magu district; to identify the challenges of cooperative unions to peasants; in Kwimba and Magu districts. The data for this study were collected from 51 respondents who included 40 peasants, 6 village cooperative union leaders, 2 cotton ginnery managers 1 Regional administrative officer and 2 Nyanza Cooperative Union leaders. Methodology of this study drew on qualitative approach based on different methods of data collection such as interview, questionnaire, focus group discussion and documentary review. The study revealed that, cooperative unions in Mwanza region benefited greatly the peasants including struggling and finally attainment of independence in Tanganyika in collaboration with elite class, provision of education to peasants and supplying of agricultural inputs to peasants. However cooperative unions in Mwanza region from 1920s to 2000s are facing various challenges which include privatization policy under globalization which has left peasants frustrated without a special organization to chain their problems. Currently, Private companies have dominated the peasant market for their agricultural produce without granting them subside. The study recommended that, the government should grant peasants with subsidies and prepare an enabling environment for peasants to acquire inputs on reasonable credit. Nyanza cooperative union and other cooperative unions in Tanzania should be re- established and introduce farm class for peasants. Further studies should be conducted to reveal the contribution of private companies towards improving peasant’s welfare in today’s world of globalization.