Aims: In this study, sediment size distribution and its statistical properties are studied in the rip channel, and its surroundings in the Royan marine ecosystem lied in the southern part of the Caspian Sea.  
Materials & Methods: Three rip current channels were selected every eight investigating months. Sediment samples were collected from inside each rip channel and its surrounding areas. The statistical indices, viz., D₅₀, mean, skewness, and sorting, have been calculated for sediment grain size parameters. Finally, a general linear model and unpaired t-test were used to perform statistical comparisons of grain size characteristics between the rip channel and its surrounding area.
Findings: In May, June, and July, the medians of sediment grain size were significantly higher in the rip channel (202.7, 168.9, and 174.5mm, respectively) compared with its surrounding areas. In general, the mean sediment grain size was significantly higher in the rip channel (193.1mm) than the control area (176.3mm). In May, June, and July, the highest values of the mean grain size of sediments were related to the rip channel (226.9, 178.5, and 183.2mm, respectively).
Conclusion: The rip channel contains sediments with coarser grains than the surrounding area. The rip current leads the median and mean of sediment size distribution in the rip channel to move toward the larger sizes. Moreover, the skewness is a more sensitive factor to environmental changes of the channel and its surrounding area than the other sediment properties, emphasizing consideration in the studies.