In today’s competitive environment, gaining the competitive advantage is one of the most fundamental challenges to managers. Nowadays, ‘human resources’ have been identified as one of the most important resources for creating competitive advantages in which those employees who are viewed as a source of knowledge shall gain more value in the organization. The extent of importance and value the knowledge workers receive in an organization, leads to a strategy known as knowledge preservation.Researchers have found that, what lead to the creation of competitive advantage is employee’s knowledge and the process of its sharing. Managers try to develop knowledge sharing on one hand, while employees try to keep their knowledge secret on the other hand. This paradox leads to a different approach between human resources and managers in hoarding or sharing knowledge. The solution proposed in this paper for aligning these two different approaches, is using the factors that cause human resources to be volunteered for sharing their knowledge with others. In this study, motivations are introduced as factors that lead to human resources knowledge sharing, on a voluntary basis. After reviewing literatures and theories of motivation, and using the questionnaire survey method, effective motivational factors in knowledge sharing were identified in an industrial-research organization in Tehran then ranked by using Friedman method. The results showed that in knowledge sharing, intrinsic motivational factors have a higher priority rather than extrinsic motivational factors.The results also declared that “friendly and sincere relations” and “job promotion” are the most important effective intrinsic and extrinsic motivational factors in knowledge sharing.