Scanning tunneling microscopy (STM) observation of Y-branched carbon nanotubes produced by the arc-discharge method is reported. A drilled out graphite rod filled with a nickel/yttrium particle mixture was used as anode in the arc chamber under He atmosphere of 660-mbar pressure. Straight multi-wall nanotubes and asymmetrical Y-branches were found in a sample taken from the cathodic deposit. As measured by STM the Y-junctions have low apparent heights in the range of I nm. This may be an indication that these nanotubes have only few walls, or possibly they are single-walled. The asymmetrical Y-branches found in this experiment may be related to the additional use of metals or/and to changed temperature conditions on the cathode side due to the switch-off of the cathode water-cooling. (C) 2002 Elsevier Science B.V. All rights reserved.