Photothermal metallic nanoparticles have attracted significant attention owing to their energy-conversion properties(1-4). Here, we introduce an optofluidic application based on a direct optical-to-hydrodynamic energy conversion using suspended photothermal nanoparticles near the liquid-air interface. Using light beams with submilliwatt power, we can drive and guide liquid flow in microfluidic channels to transport biomolecules and living cells at controlled speeds and directions. Previously, a variety of methods for controlling microscale liquid flow have been developed owing to the increasing interest for microfluidics-based biochemical analysis systems(5). However, our method dispenses with the need for complex pump and valve devices(6-8), surface chemistry(9,10) and electrode patterning(11-14), or any other further effort towards substrate fabrication(15,16). Instead, our optofluidic control method will allow the fabrication of all-optical large-scale integrated microfluidic circuits for biomolecular and cellular processing without any physical valve or mechanical pumping device.