A new distinct cultivar of Osteospermum plant named `Sunny Maxima`, characterized by its plant height averaging 16 cm, and plant diameter averaging 25 cm; thicker and sturdier stems; large, composite, daisy type inflorescences measuring up to 8 cm in diameter; fully opened inflorescences with striking red-purple ray florets with light red-purple bases and disc florets with gray-purple tips and a light purple basal tube; and mature foliage color of green, RHS 137A (upper side) and yellow-green, RHS 147B (under side).