In order to examine the nutritional value of prickly pear(Opuntia humifusa), contents of ash, protein, fat, minerals and vitamins were determined on freeze-dried stem, fruit, seed and root from plants harvested in autumn. The average moisture contents for stem, fruit, seed and root were 67~87%. Crude ash content determined on dry weight basis was 2~3%. Crude protein existed mostly in seed(2.95%) and root(2.37%). Crude fat was detected mainly in seed(4.49%). Contents of major minerals(mg/100 mg dry weight) was generally higher in stem. Ca in stem(4,142.30) and fruit(2,790.86) were much higher than in seed(43.37). P in stem, seed and fruit were 448.19, 263.20 and 161.59, respectively. Stem also displayed more abundant Mg(1,110.86), Zn(35.62) and Mn(37.07). However, fruit contained higher amounts of Fe(13.38) and Se(0.15). Vitamin A was negligible in all plant parts. Vitamin E contents in fruit and stem were 1.78 mg and 1.22 mg/mg dry weight, respectively. Vitamin C was detected mostly in fruit(445.40) and stem(260.94). Use of a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide-based microtiter assay of cell viability demonstrated an anti-proliferative effect of O. humifusa extract on the MCF-7 estrogen-dependent human breast cancer cell line.