Tungsten trioxide films were prepared by sol-gel method using peroxotungstic acid (PTA) as the precursor sol with Triton X-n (with n = 45, 100, 305, 405, 705) surfactants. Physical (morphology, film thickness, surface roughness and crystallite, grain and particle size) and photo-electrochemical (PEC) properties of the synthesized films were characterized. The physical characterization showed a clear correlation with surfactant size. Most importantly, the correlation between grain size and surfactant size followed a monotonic equation. Similarly, the PEC properties were strongly correlated to surfactant size. The best performance was observed with the smallest surfactants. The highest photocurrent density of 2.10 mA cm-2 at 1.6V (vs. RHE), was produced by Triton X-45. Results presented a simple method to control the grain size and performance of W03 semiconductor. 2014 Elsevier BY. All rights reserved.