The aim of the present study was to predict organic matter (OM) loss in Kojor Watershed which is a hyrcanian ecosystem. For this purpose, discharges, suspended sediment (SS) and OM loss resulting from storm events were sampled at one fixed point of the river using a manual sampler. Results showed that soil erosion rate during the sampling period were dramatically affected by the loss of OM. Also, the results of modeling among OM loss, SS and discharge indicate that OM loss was not estimated by the discharge, while SS can estimate the loss of OM with a determination coefficient and estimation error of of 95% and 24%, respectively. These results could facilitate the application of methods obtained in the present study to other areas with similar conditions.