Informal group came into existence through the interaction of people as a result of socialization. When individual meet and interact with one another, there is the tendency for individuals with similar interest and characteristics to form powerful cohesive groups in order to obtain organizational objectives. It therefore, the objective of this research was find out the relationship that existed between informal groups activities on productivity levels in organizations for effective management of the informal groups in Nigeria organizations. A review of the related interactive was made to provide a sound theoretical background of the concept of informal groups. This was done by review of work previously done by scholars on the concept of informal groups. By making use of a case study, questionnaires was distributed or rather administrated to the workers at University of Nigeria Teaching Hospital, Enugu. The data collected from the filed was analyzed, the hypotheses, which were formulated, were tested through the use of statistical models. The findings of the research were that workers were found to be keenly interested in belonging to informal groups in their work places such as the trade unions. They agreed that they derive benefits groups offered by the groups to workers given the opportunity to work for their benefits. Workers should realize their primary objectives through group association. Managers should realize that team spirit is the important characteristics of informal groups which motivate them to be effective in organization. Informal organization are not officially recognized and do not have any space in organizations organigram. My conclusion is that since informal organizations continue to exist and can not be stopped or terminated in any set up, it should continue to be accommodated as much as it does not adversely affect the attainment of organizational goals. During recruitment, selection and orientation, new employees should be made to join informal groups such as trade union or any other, this makes the workers to socialize and adopt quickly and better to the values existing in the organization. More consultation of the informal groups by the management should be encouraged and suggestions made by the workers be utilized as this motivates the workers more for greater performance.