We developed dual-modality microscope integrating photoacoustic microscopy (PAM) and fluorescence confocal microscopy (FCM) to noninvasively image hemoglobin oxygen saturation ( ${\mathrm{sO}}_2$ ) and oxygen partial pressure ( ${\mathrm{pO}}_2$ ) in vivo in single blood vessels with high spatial resolution. While PAM measures ${\mathrm{sO}}_2$ by imaging hemoglobin optical absorption at two wavelengths, FCM quantifies ${\mathrm{pO}}_2$ using phosphorescence quenching. The variations of ${\mathrm{sO}}_2$ and ${\mathrm{pO}}_2$ values in multiple orders of vessel branches under hyperoxic (100% oxygen) and normoxic (21% oxygen) conditions correlate well with the oxygen–hemoglobin dissociation curve. In addition, the total concentration of hemoglobin is imaged by PAM at an isosbestic wavelength.