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We proposed a new type of passive saturable absorber (SA) based on tungsten trioxide (WO 3)-polyvinyl alcohol (PVA) film for generation of soliton mode-locked pulse in the erbium-doped fiber laser (EDFL) cavity. The WO 3-PVA has a modulation depth of 20% with a saturable intensity of 0.04 W/cm 2. The new SA film was integrated into the cavity to realize a stable mode-locked pulses operating at 1565.08 nm within a pump power range from 50 mW to 225 mW. The pulse repetition rate and pulse width of the soliton laser was 1.85 MHz and 2.69 ps, respectively. The pulse energy of 1.14 nJ and peak power of 0.67 kW were obtained at the maximum input pump power of 225 mW. These results indicate that WO 3 is a promising nonlinear optical material for application in generating ultra-fast mode-locked laser. This is the first time that WO 3 was utilized as SA in the 1.5 μm region.