Copao (Eulychnia acida Phil.) is an endemic arborescent cactus restricted mainly to the semi-arid Coquimbo Region (29°54’28" S, 71°15’15" W), Chile. The area of distribution is from sea level to 1200 m.a.s.l. The edible fruit called rumpa is generally round, with green or pink peel and small scales on its surface, showing wide variability in size and weight. The aim of this work was to characterize the rumpa harvested in January 2009 and 2010 in three sectors of Coquimbo Region to determine chemical and nutritional composition in three fractions: pulp with seeds, juice, and peel. The research showed that this fruit is a good natural source of mainly soluble dietary fiber, which has a jellied texture and is present in the three fractions analyzed: 2% for juice, 3% for pulp with seeds, and approximately 5% for peel, making it potentially a good source of hydrocolloids for the food industry. The fruit is also a good source of vitamin C; around 55 mg 100 g-1 in peel, and 30 mg 100 g-1 in pulp with seeds and juice, values considered high compared to 18 mg 100 g-1 for prickly pear (Opuntiaficus-indica [L.] Mill.) The main minerals were: K, Mg, Ca, and P. Total polyphenols and betalain pigments were also determined in the pulp with seeds and pink peel fractions, respectively. The nutritional characteristics, together with its high water content of around 96%, make rumpa a promising raw material for agro-industrial development of natural juices or isotonic drinks. This characterization helps in the recovery of an endemic native species by reducing potential threats to destroy wild populations of E. acid, especially near agricultural areas, and by promoting habitat conservation of the species in the region.