A new and distinct cultivar of Chrysanthemum plant named `Yoessex`, characterized by its upright, outwardly spreading and uniformly mounded plant habit; moderately vigorous growth habit; freely branching habit; dark green-colored foliage; uniform, freely and early flowering habit; daisy-type inflorescences with purple-colored ray florets and green-colored disc florets; and excellent postproduction longevity.