Introduction: Anaemia is the commonest haematological complication in cancer patients with aetiology usually multifactorial. The cut-off value for anaemia vary from centre to centre but a haemoglobin (Hb) level of 12g/dl in male and 11g/dl for female is usually acceptable in most Radiation Oncology Centres in Nigeria for therapeutic purposes. Administration of radiotherapy without adequate haematological support may tilt the patient into clinical anaemia. The study aims to ascertain the effect of radiotherapy on the haemoglobin level of cancer patients undergoing therapy. Materials and Methods: Patients with solid tumours with intent for radical treatment were recruited within a period of 8 months. Informed consent of participants was obtained. Demographic characteristics of the cancer patients and their various oncologic diseases were gathered. Baseline Hbandblood film pictures were measured on the first day of consultation then once every 2 weeks for 6 weeks. Data collected were summarized and presented in tables. Results: Out of 63 cancer patients, 92.1% were female. Mean and median ages of patients were48.55and 50 years respectively. Breast 47.6% (30) was commonest tumour while 74.6%(47) presented with stage III disease. Prevalence of anaemia in the study was 42.9%. At the end of therapy 55.6% (63) cancer patients had their Hb level between 11.52 – 12.13g/dl. Conclusion: Prevalence of anaemia in cancer patients undergoing radiotherapy was high. Female group dominated the study population. Patients had a downward trend in their Hb level as their treatment progressed thereby calling for need early identification and timely intervention.