Thin film composite (TFC) membranes are considered a preferred platform for forward osmosis (FO) wherein the selective and support layers can be tailored independently for preferred chemistry and structure. TFC hollow fiber membranes in particular have garnered interest because of their high packing density. In previous studies, TFC hollow fiber membranes were made by forming the selective layer via in-situ interfacial polymerization onto a porous supporting layer. These studies, however, have not examined how the surface properties of the support layer, the pore size in particular, impact the selective layer formation and its properties. In this study, we conducted a systematic investigation on the influence of support layer pore size on the osmotic performance of TFC hollow fiber FO membranes. A series of commercially available ultrafiltration membranes with similar physical and chemical properties but different pore sizes were employed as the support layers. The resulting roughness of the selective layer was found to be dependent on support layer pore size. Osmotic flux tests revealed that the membrane performance is dependent on this roughness with rougher membranes exhibiting higher fluxes in many cases. Aside from elucidating the impact of support layer pore size on osmotic performance, we also demonstrated the potential of making high performance FO membranes using existing commercial hollow fiber ultrafiltration membranes.