We report an experimental observation of staircase pulses generated from an Er:Yb co-doped fiber laser operat-ing in the anomalous dispersion regime. The staircase pulses consist of two distinct square pulses associated withdifferent wavelengths in a dual peak spectrum and they exhibit particular temporal characteristics. To establish atheory behind the experimental results, we simulate numerically the fiber oscillator by using a master equationand taking into consideration the gain inhomogeneities as well as other nonlinear variables.