Abstract: A surface treating composition for treating long glass fibers for use in making long fiber-reinforced resin composites and methods for preparation and use thereof are provided. The surface treating compositions comprise(i) a wetting agent in an amount ranging between about 3 and about 40 wt. %, said wetting agent having a formula: ##STR1## wherein A=4-12; B=2-10; n=2-6; m=20-40; and R=CH.sub.3 or C.sub.2 H.sub.5 ; and a thermoplastic resin in an amount ranging between about 1 and about 40 wt. %, said thermoplastic resin is selected from the group consisting of polyamide polymers, polyamide copolymers, polyalkylcarbonate polymers, polyalkylcarbonate copolymers, and mixtures thereof. Reinforced thermoplastic composites having the treated glass fiber have excellent mechanical and uniform fiber dispersibility properties.