Uniform one-dimensional (1D) structures of o-phenylenediamine (oPD) oligomers are obtained by direct mix of AgNO3 and oPD aqueous solutions at room temperature. The formation of the 1D structures involves two stages: (1) oxidation of oPD by AgNO3, yielding individual oPD oligomers; and (2) self-assembly of the oligomers, forming the 1D structures. Upon decreasing medium pH, the 1D structures can break-apart to form individual oligomers, or vice versa. It is also found that both the concentration and molar ratio of reactants can influence the morphology of the structures thus formed.