Previous studies have reported anticancer activity for Carica papaya leaves and fruit. However, to date there are no reports on the anticancer properties of C. papaya roots. The current study was undertaken to test whether C. papaya root extracts inhibit the proliferation of two extensively studied human carcinoma cell lines: Caco-2 colorectal cancer; HeLa cervical cancer. Furthermore, roots grown in an in vitro bioreactor system under controlled conditions were tested in parallel with field grown roots of the same papaya clone to determine if both have similar anti-proliferative properties and efficacies. The roots were extracted with solvents of varying polarity and investigated using an MTS based anti-proliferative assay. The methanolic and aqueous C. papaya root extracts were potent inhibitors of Caco-2 and HeLa proliferation. No significant difference was noted between the field grown and bioreactor grown roots. The anti-proliferative activity of the methanolic and aqueous root extracts against Caco-2 and HeLa carcinoma cells indicates their potential in the development of novel chemotherapies against some types of cancer.