A new and distinct plum tree variety, Prunus salicina, 'Suplumtwentysix' characterized by consistent heavy production of large (61 mm), reddish-black plums with amber-colored flesh, which ripen in late May to early June in Kern County. The eating quality of plums produced by 'Suplumtwentysix' is relatively good for the early season, with juicy sweet-tart flesh and mildly tart skin.