The study aim was to explore the anatomy, histopathology, and molecular biological function of the fascias posterior to the interperitoneal colon and its mesocolon to provide information for improving complete mesocolic excision. To accomplish this aim, we performed intraoperative observations in 60 interperitoneal colon-cancer patients accepted for complete mesocolic excision and conducted local anatomy observations for five embalmed cadavers. An additional two embalmed child cadaver specimens were studied with large slices and paraffin sections. Ten of the 60 patients were examined with a lymph node tracer technique in vivo, while fresh specimens from these patients were assessed by histopathological examination and transwell cell migration assays in vitro. The anatomical and histopathological findings showed that the fascias posterior to the interperitoneal colon and its associated mesocolon were composed of two independent layers: the visceral and parietal fascias. These two fascias were primarily composed of collagen fibers, with the parietal fascia containing a small amount of muscle fiber. The in vivo test showed that the visceral fascia surrounded the colon and its associated mesocolon, including vessels and lymphatics, and that it had no lymphatic flow through it into the rear tissues. Moreover, the in vitro assays showed the visceral fascia was able to block tumor cell migration. Although many surgical scholars have known of the existence of fascia tissue posterior to the intraperitoneal colon, the detailed structure has been ignored and been unclear. As shown by our findings, the visceral and parietal fascias are truly formed structures that have not been previously reported. A thorough understanding of fascial structures and the function of the visceral fascia barrier in blocking tumor cells will facilitate surgeons when performing high-quality complete mesocolic excision procedures.