An apparatus for manufacturing carbon nanotubes is provided. The apparatus includes: a reaction chamber having an inlet and a outlet; a heater for elevating an interior temperature of the reaction chamber; and a gas guiding member coupled to the inlet and configured for introducing a carbon-containing gas into the reaction chamber, the gas guiding member including a gas-exiting portion arranged in the reaction chamber, the gas-exiting portion having a cavity defined therein and a flat perforated top wall, the perforated top wall being configured for supporting a substrate thereon and defining a route allowing the introduced carbon-containing gas to flow in a direction substantially perpendicular to a main plane of the substrate.