Based on an organic nonlinear optical material, Maleic Acid-Doped Polyaniline (MADP) Saturable Absorber (SA), a stable Q-switched pulse operation was realized in an erbium-doped all-fiber laser for the first time. In this experiment, the modulation depth and saturable absorption intensity of the MADP-SA were measured at 13.9% and 0.336 MW/cm² using the twin detector technique, respectively. The MADP-SA is inserted into the fiber resonator in the form of a thin film sandwich. The stable Q-switched pulse operation are achieved with the repetition rate range from 33.78 kHz to 87.01 kHz, the narrowest pulse width of 2.29 μs and the maximum single pulse energy of 54.64 nJ. MADP can be considered as a good candidate for pulsed fiber laser applications and other optoelectronic devices.