A near infrared fluorescent contrast agent comprising a compound having three or more sulfonic acid groups in a molecule, and a method of fluorescence imaging comprising introducing the near infrared fluorescent contrast agent of the present invention into a living body, exposing the body to an excitation light, and detecting near infrared fluorescence from the contrast agent. The near infrared fluorescent contrast agent of the present invention is excited by an excitation light and emits near infrared fluorescence. This infrared fluorescence is superior in transmission through biological tissues. Thus, detection of lesions in the deep part of a living body has been made possible. In addition, the inventive contrast agent is superior in water solubility and low toxic, and therefore, it can be used safely.