This study aimed to characterize the different parts of Carica papaya (ripe and unripe papaya, leaves and seed), through their proximate composition, total antioxidant activity, and in vitro antiproliferative activities. Both macronutrients and micronutrients were determined using standard AOAC methods of analysis, while vitamin analyses were determined by high performance liquid chromatography (HPLC). Results showed that the ripe papaya had the highest antioxidant activity (84.04%) followed by unripe papaya (81.35%), leaves (78.03%) and the least was seed (75.35%). The phenolic content was in the order of leaves > unripe papaya > ripe papaya > seed. HPLC analysis showed that papaya leaves exhibited the highest ascorbic acid and β-carotene content (85.60 and 3.86 mg/100 g respectively), while the seeds had the highest Vitamin E content (4.09 mg/100 g). Results obtained from cytotoxic activities showed that MCF-7 (hormone dependent breast cancer) and MDA-MB-231 (non-hormone dependent breast cancer) cell cultures were significantly inhibited by the extract. The antioxidant and antiproliferative activities of different parts papaya extracts indicate that the consumption of the whole fruit, ripe and unripe papaya, leaves and the seed supplies the important quantities of numerous necessary nutrients for human diet which includes vitamins A, C and E.