A filamentary plasma jet was produced by a cylindrical dielectric-barrier discharge ( DBD) equipped with a thin quartz tube. This plasma jet consists of many filaments, and the filaments bifurcate into thinner branches close to the ground electrode. Only a single filament is produced in each current pulse, and this filament is distorted in the long gas gap. The maximum electron density in the filament is on the order of 10(15)cm(-3). Optical emission examination shows a decrease of optical emissions from OH and Ar but an increase of optical emissions from N2 along the plasma jet. The vapor in the working gas argon rather than in the ambient air dominates the optical emissions from the de-excitation of OH along the plasma jet. Near the ground electrode, the nitrogen emission spectra mainly resulted from the direct electron effect on the ground state or metastable nitrogen and the collisions between nitrogen metastables. The rotational temperature is lower than the vibrational temperature but much higher than the room temperature. This feature makes the filamentary plasma jet only suitable for processing samples bearing high temperature.