Objective: The present study was designed to investigate in vitro cytotoxic effect of aqueous extract from whole Cuscuta chinensis on human hepatocellular carcinoma (HepG2), biopsy xenograft of pancreatic carcinoma line-3 (BxPC-3), and children human bone osteosarcoma cell line (U2OS). Materials and Methods: The anticancer effectiveness of the methanol-watery extract of C. chinensis Lam. was determined by using methyl tetrazolium bromide test (MTT) assay against cancer cells by using suspensions of BxPC-3, HepG2, and U2OS cell lines. The inhibitory concentration (IC50) was tested for each cancer cell line. BxPC-3, HepG2, and U2OS cell line death percent after incubation with extract for 24, 48, and 72-hours interval was compared with cisplatin death percent. Results: The results showed that the IC50 of Cuscuta extract for BxPC-3, HepG2, and U2OS cell lines was 13, 6.5, and 0.73 μg/mL, respectively. The HepG2 cell line death%, when treated with 50 μg/mL Cuscuta extract at 24, 48, and 72-hour time interval, was 90.41, 91.45, and 92.93%, while cells were treated with 15 μg/mL cisplatin, the death percent was 88.8, 93.7, and 96.61%, respectively. The BxPC-3 cell line death%, when treated with 50 μg/mL Cuscuta extract, was 51.46, 83.37, and 91.28%, respectively, and when treated with 15 μg/mL cisplatin was 81.64, 88.02, and 96.67%, respectively. The U2OS cell line death%, when treated with 50 μg/mL Cuscuta extract, was 69.43, 69.75, and 88.89%, and was 74.1, 84.61, and 93.39%, respectively, when treated with 15 μg/mL cisplatin. Conclusion: The methanol-watery extract of C. chinensis Lam. may have a potential role as an adjunct therapy for cancers in the future.