According to the instructions of Iran's National Corona Response Committee in the Iranian Ministry of Health and Medical Education, patients undergoing treatments for their cancer are prioritized in Covid-19 vaccination. The present study was therefore conducted to investigate the toxicity and acute side-effects of a Covid-19 vaccine in cancer patients presenting to Medical Oncology Clinic of Kermanshah University of Medical Science. After excluding the patients with active infection and the recently-infected ones with Covid-19, they underwent the vaccination. The patients with cell counts exceeding 3,000 received two doses of the vaccine with a 21-day interval and treatment of their underlying disease was postponed for 7 days. The side-effects were mild and tolerable and included fever (case 10), pain at the injection site (7), dizziness (7), body pain (6), abdominal pain (6), myalgia (6), headache (6), chills (3), shortness of breath (3), diarrhea (1), runny nose (1) and dryness of the throat (1). No significant toxicity was reported in the patients who were safely vaccinated under the supervision of the medical oncology clinic.