An 8-ounce serving of canned, unsweetened orange juice contains 458 milligrams of potassium, according to the USDA's National Nutrient Database for Standard Reference. The exact amount of potassium can vary based on the form in which the orange juice is preserved.
Potassium is an important mineral, used by the body to maintain a proper balance of fluids, to moderate blood pressure and to help muscles contract. Potassium also promotes healthy heart and kidney function. The recommended daily intake for an individual who is at least 14 years old is 4,700 milligrams per day, and a serving of orange juice supplies approximately 10 percent of this daily need.