Bring 4 cups water to a boil over medium-high heat. Stir in 1 cup sugar, and cook, stirring constantly, 1 minute or until sugar dissolves; remove from heat. Stir in 1/3 cup lemon juice, tea bags, and mint leaves. Cover and let stand 1 hour.
Remove tea bags from water, squeezing gently; discard tea bags. Pour tea mixture through a wire-mesh strainer into a 2-qt. pitcher, discarding mint leaves. Stir in 4 cups cold water. Cover and chill at least 1 hour. Serve over ice.