In forest ecosystems, rainfall is partitioned by forest canopies intothroughfall (TF), stemflow (SF), and interception loss (I). In the present study the partitioning of rainfall was studied in a natural chestnut-leaved oak (Quercus castaneifolia C.A.Mey) forest situated in the Caspian Forest,north of Iran. Measurements were carried out on a rainfall event basis in a 0.12 ha sample plot of an oak forest, during 2009 and 2010, from July to October. Gross rainfall (GR) was measured in an open area close to the study plot. Thirty five throughfall collectors were randomly placed beneath the oak forest canopies and SF was collected from nine selected oak trees using the spiral type SF collection collars. The cumulative GR amount of 28 events was 651.5 mm. The amount of cumulative GR transformed into TF, SF and I were 489 mm, 2.6 mm, and 159.9 mm, respectively.On the event scale average ratios of TF:GR, SF:GR, and I:GR were75%, 0.4%, and 24.6%, respectively. A fairly strong negative correlation was observed between I:GR and GR. As the intensity of the rainfall events increased, the interception loss in the oak forest canopies decreased.We concluded that interception in the oak forest represents a remarkable percentage of GR and it was strongly affected by the amount of GR.