The statistical characteristics and downstream fining of River Osun in southwestern Nigeria were studied, to determine the variation in particle sizes,contributory effects from tributaries,and the deposition characteristics of these sediments.A total of 10 samples were collected along the River Osun, from Osogbo to Omitutu, covering a total distance of 140 km. Sampling was done within the river bends, meanders, and exposed bars adopting the purposive sampling method. Each sample was washed, through a 0.063mm sieve and mechanically sorted into a set of US mesh sieves of 2.360, 2.00, 1.00, 0.50,.250, .125 and 0.063 mm respectively and a receiving Pan (Wentworth Classification) using a Ro-tap shaker inthe Soil Mechanics Laboratory of National Water Resources Institute, Kaduna. The graphic mean of River Osun sedimentsranges between -0.7 to 0.93ф with an average of 0.07ф. This indicates a very coarse to less coarse sand. It contains 40.79% fine gravel,20.90% coarse sand, 21.29% medium sand and fine sand account for 16.90%. This showed that particles are carried as bed load and are either close to their source or mixing from tributaries.The sorting varied from 0.74 to 1.25ф, with an average of 1.26ф. It indicates moderately to poorly sorted sand,which implies a rapid deposition or lateral addition of sand from other sources.The skewness values range from -0.06 to 0.42ф (platykurtic to leptokurtic).This reflects the flow characteristics of the deposition medium, which range from low to high kinetic energy of sediment transport causing deposition.The downstream fining showed a virtual departure from an exponential order; the effect could be attributed to the lateral addition/mixing, as well as anthropogenic factors like the construction of a dam, irrigation, and sand dredging along the channel.This study can provide the baseline information in the study of transportation, deposition,and grain sizes of heavy minerals along the river channel.