The aim of the research is to study the impact of informal communication and its dimensions on the efficiency and effectiveness of intellectual capital to achieve sustainable development,The organization's possession of a distinguished strategic intellectual capital is the main source for achieving sustainable development and competitive advantage in any country, It also depends on the success of organizations in achieving their goals It requires the existence of a management capable of adjusting its organizational structure in accordance with its characteristics and adopting an administrative approach that allows it to make flexible and quick reactions towards its constantly evolving competitive environment. In this research, he highlighted the informal communication that is overlooked in organizations and the possibility of investing in it and benefiting from it in serving the goals of the organization and converting it into an added value for it and its intellectual capital. The researcher used the descriptive analytical approach and the survey list method to collect the necessary data from the employees of some real estate investment companies  , The results resulted in the validity of the research hypothesis and its acceptance that there is a statistically significant correlation between intellectual capital and informal communication, as the variables (providing appropriate work conditions - cooperation between others - raising the level of capabilities) affect the efficiency and effectiveness of intellectual capital, The research also recommends adopting informal communication as an effective administrative method to be followed and trying to employ it and benefit from it in creating a suitable work environment for it and its human capital.
Keywords: informal communication , intellectual capital , sustainable development .