Introduction: The quality of nursing care is affected by nurses' knowledge and experiences that they attained in nursing practice these knowledge and experiences improvement could be relied on acquisition knowledge from colleagues. Aim: this study was done for assessing effect of perceived knowledge support from the organization by nurses on their professional knowledge sharing. Methods and Materials: This causal study was done in one of hospitals in Yasouj city in (2014) as a case study. All of nurses who worked were selected (104). For data gathering were used two questioners Perceived Knowledge Organizational Support (Donate & Guadamilla 2011) and Knowledge Sharing Behaviors (Huang & et., al, 2013). Divergent content validity test were (0.61 – 0.67) and &alpha- Chronbach for reliability were (0.71 and 0.76) respectively. Data gathered by (98) questioners ( 94% returned) were analyzed using structural equation modeling based on variance by Smart PLS and descriptive tests by SPSS. Results: Findings showed that organizational knowledge-oriented atmosphere, had significantly positive effect on nurses’ motivation to share their knowledge (&beta=0.41 T=3.86). But this effect was not significantly in the knowledge-oriented supervisory and human resource management practice (T<1.96). Furthermore, nurses’ motivation to share their knowledge (&beta=0.52 T=4.06) and availability of opportunities to share the knowledge (&beta=0.30 T=2.64), have significantly positive effect on their knowledge sharing behaviors. Conclusion: Nurse managers would be increased nurses' motivation for sharing professional knowledge by providing sufficient opportunity for knowledge sharing for them and also organizational supportive atmosphere creation. It must be based on confidence between managers and staff that knowledge sharing adopted as a value in organization.