A conducting polymer, polypyrrole with fractal patterns, has been formed by a constant-current polymerization method. The patterns of growth on the surface of the cell have been classified into three types; needle-like, DLA-like, and broad leaf-like. The type of pattern formed by polymerization with constant-current control varied with time since the effective applied voltage decreased with time. The change in the pattern has been estimated numerically by the fractal dimension.