A simple sensor based on glassy carbon electrode (GCE) modified by chitosan/polyaniline (PANI) nanocomposite has been studied. The casted nanocomposite film on GCE was prepared from formic acid, acetic acid and citric acid aqueous solutions. The morphology and electrocatalytic activity of chitosan/PANI nanocomposite were characterized by scanning electron microscope (SEM), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). CV results revealed that the polyaniline in the chitosan/PANI film exhibited electrocatalytic activity to redox reactions of potassium ferricyanide (K3Fe(CN)6) used as probe. Among the three acids, chitosan/PANI casted by formic acid exhibited the most appropriate polyaniline dispersion in chitosan film, which resulted in the highest electrocatalytic activity. Therefore, chitosan/PANI nanocomposite casted on GCE via formic acid was used as working electrode to detect dopamine (DA). The biosensor provides a linear DPV response in the range of 0.25mM to 1.75mM for DA detection.