At the present time, to minimize friction and to control wear in machines elements are used with lubricating oil manufactured by advanced technologies. The high performance of lubricating oils is provided by oil additives. Additives improve the lubricating ability of the base oils by either enhancing the desirable properties, which is already present, or obtaining new properties. The decreasing of the world's finite resources of mineral oil and the increasing environmental awareness have increased investigations about new environmental lubricant and additive candidates. Cottonseed oil (CSO) with Turkish origin was studied as an additive candidate in the presented study. Investigation of the effect of CSO addition to base oil on the friction coefficient was aimed in the journal bearing under static loading at ambient room temperature (25degreesC). Tests was performed by using base oil (SAE 20W50) alone and lubricating oil at concentration ratios 2.5, 5, and 10 vl % additives as CSO at five different speeds and three different loads. The experimental study clearly showed that the CSO could be used as an additive of friction modifier.