The present invention provides a dual-purpose photoacoustic tomography (PAT)/ultrasound contrast agent comprising: (a) a micro-bubble containing gas and porphyrin therein; and (b) nanoparticles bound on a surface of the micro-bubble and containing a drug. The contrast agent of the present invention can be used in both the ultrasound diagnosis and the photoacoustic image diagnosis, and can significantly increase the accuracy of photoacoustic images.