The vitamin could potentially be a safe, effective and low-cost treatment for ovarian and other cancers, they said.
Researchers said vitamin C has long been used as an alternative therapy for cancer. It is known that the human body quickly excretes the vitamin when it is taken by mouth.
Scientists at the University of Kansas in US said that when given by injection vitamin C is absorbed into the body, and can kill cancer cells without harming healthy ones.
The researchers injected vitamin C into human ovarian cancer cells in the lab, into mice, and into patients with advanced ovarian cancer, the BBC reported.
They found ovarian cancer cells were sensitive to vitamin C treatment, and normal cells were unharmed.
The treatment worked well with standard chemotherapy drugs to slow tumour growth in mouse studies.
A small group of patients also reported less side-effects when given vitamin C alongside chemotherapy.
"Patients are looking for safe and low-cost choices in their management of cancer," co-researcher Dr Jeanne Drisko said.
A potential hurdle is that pharmaceutical companies are unlikely to fund trials of intravenous vitamin C because there is no ability to patent natural products, the report said.
"We believe that the time has arrived for research agencies to vigorously support thoughtful and meticulous clinical trials with intravenous vitamin C," said lead researcher Qi Chen.
The study was published in the journal Science Translational Medicine.