This article in the results of research projects which is called ''effect of environment on organizational structure by the emphasis on knowledge management in 2011 .The objectives of the research were to evaluate the extent of environmental uncertainty, dimensions of organization structure, and the degree of Knowledge management usage within public Organizations. Furthermore, the impact of environmental uncertainty and knowledge management on structural dimensions in statistical society considered. In terms of methodology, this paper conducted based on a descriptive, and applied, and the data's accumulation is field. Populations of target group are public organizations of Guilan province (the major province in Iran), and 69 organizations were recognized as a sample. Questionnaire tool was used for gathering the data. The data were analyzed by soft wares LISREL and SPSS. Findings of this paper support the ability of Knowledge management as a modifier in relation between environmental uncertainty and structural characteristics. In addition, the environmental uncertainty increases the organizations' need to develop of knowledge management capabilities. This case reveals the necessity of changes about the organizational structure more .