The effect of decane-functionalized reduced graphene oxide (decane-rGO) was studied on the performance of polyacrylonitrile (PAN) ultrafiltration membranes. The results showed that the decane-rGO/PAN membranes had greater salt rejections relative to their corresponding GO/PAN membranes, confirming superior performance of modified decane-rGO particles. Also, the membrane with 0.2 wt% decane-rGO exhibited maximum water flux and appropriate salt rejection. The field-emission scanning electron microscopy (FE-SEM) micrographs illustrated that the sponge-like pores in the pristine PAN membrane were changed to a finger-like structure in the membrane containing up to 0.2 wt% of decane-rGO and the vertical holes were converted to horizontal holes by further increasing the decane-rGO concentration in the polymer matrix.