The electrochemical behavior of C60 and C70 films on glassy carbon electrode with tetramethylammonium perchlorate in acetonitrile solution was investigated by cyclic voltammetry(CV). The cyclic voltammogram of such films showing an unusual hysteresis suggested that large structural changes occur on reduction. We described the first well-resolved cyclic voltammogram of C60 and C70 films with small size cations N(CH3)4+ by using an ultramicroelectrochemical cell technique. These results, accompanied by electrochemical quartz crystal microbalance(EQCM) method, led the doping process of NR4+ and dissolution process of fulleride being able to be characterized in detail to understand the structures as well as phases of doped films. Different phases of doped C60 and C70 films, such as C60n−(NR4+)m and C70n−(NR4+)m (n = 1,2; m = 0,1,2), were proposed to investigate two reduction peaks of fullerene from neutral to −2 charge.