We propose and demonstrate a Raman-assisted passively mode-locked Yb-doped fiber laser in a normal dispersion regime.A section of highly nonlinear fiber is adopted to enhance the nonlinearity to extend the bandwidth of the gain spectrum by the stimulated Raman effect.The mode-locked fiber laser emits a broad spectral bandwidth of 64 nm at the-20 dB level and a highly stable pulse operation with a signal-to-noise ratio of 77 dB.