Monodispersed crystalline CuO particles of different morphologies were synthesized by the controlled double-jet precipitation (CDJP) technique using NaOH and Cu(NO3)(2) as the reactants. The effects of temperature, reaction time, pH, and the concentrations of chemicals on the characteristics of final products were investigated. With lower [NaOH]/[Cu(NO3)(2)] molar ratios and temperatures, colloidal gerhardtite Cu-2(OH)(3)NO3 precipitated, while tenorite CuO particles of various morphologies were obtained at higher temperatures and [NaOH]/[Cu(NO3)(2)] ratios. Time resolved electron microscopy indicated that nanosized primary particles formed immediately after mixing the reactants, followed by aggregation into larger uniform particles of submicrometer size.