Hydrophilic carbon nanoonions coated with carbon nanobubbles were synthesized by long-pulse-width laser ablating of carbon black particles suspended in water. The high resolution TEM (HTREM), selected area electron diffraction (SAED) and Raman spectrometer results revealed that the crystallinity and the structure of carbon nanoonions. All analysis techniques showed that the hydrophilic properties of carbon nanoonions could be ascribed to both hydrophilic groups and carbon nanobubbles simultaneously formed on the surface of the synthesized carbon nanoonions under laser ablation, in which the carbon nanobubbles were also believed to improve the specific surface area and form more hydrophilic groups by chemical or physical absorption.