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Estimation of Origin-Destination (O-D) matrix is very important in transportation planning. This matrix contains information about travel demand between different zones of a region. In this paper, a model is proposed for estimation of (O-D) matrix using traffic counts. In the model, (O-D) matrix is estimated using traffic counts, zone populations and interzonal distances. Traffic counts, zone populations and interzonal distances are data which can be easily obtained. So, offered model is useful for the situations in which data collection process is difficult. Furthermore, the data of population and interzonal distance is important with regard to taking account of the economic aspect of interzonal trips. The fundamental principle of model has been based on modifying the initial matrix that will provide previously determined link counts. In this process, the elements of initial matrix are increased as proportional with interzonal gravity model. It has exponentiated the multiplication of population values of zones at the numerator of gravity model to the x-th power and interzonal distances at the denominator of gravity model to the y-th power. So, importance of zone populations and interzonal distances has been reflected to the model. It has been worked to minimize the link flow error while exponent values (x,y) are changed with augmentation value that will be determined according to desire. When error at posterior iteration is larger than previous iteration, algorithm is terminated. Algorithm has been written and tested a highway network that has four zones and eight links. [ABSTRACT FROM AUTHOR]