Single-walled carbon nanotubes (SWNT) in a poly(ethylene)ghycol solution are a biocompatible transporters with strong optical absorption in the near-infrared region, in which the biological tissue is almost transparent with very low absorbance. Here, antibody-functionalized SWNTs for tumor early detection with photoacoustic molecular imaging in vivo are reported. To lay the groundwork for this goal and insure system stability, images were collected in tissue simulating phantoms to determine appropriate detectable concentrations of SWNTs. Preliminary in vitro and in vivo results showed that a high contrast and a high efficient targeting of integrin positive U87 human glioblastoma tumours in mice could be achieved. The nontoxicity of functionalized SWNTs has also been demonstrated in our experiment; this feature ensures that SWNTs can be used for clinical applications. This study suggests that photoacoustic molecular imaging with antibody-functionalized SWNTs has the potential to be an effective early tumor diagnosis method.