Young Iolanta carelessly lives at the castle of her father King Rene. Her blindness doesn't bother her. The Moorish physician Ibn-Hakia is invited to cure her. However, the girl is to realize her disease becoming eager to acquire the eyesight. Poor King can't dare to tell this dramatic truth to Princess.
Count Vaudemont and his friend Robert, Duke of Burgundy lose there way and find themselves in the royal garden. Long ago being a stripling Robert was engaged to Iolanta. However, he loves Countess Mathilde of Lorraine. Quite of a sudden sleeping Iolanta attracts the sight of young gentlemen. Vaudemont's heart is won forever. Having awoken the young lady welcomes the noble knights to repose in her castle. Prudent farsighted Robert refuses, suspecting the peril impending over his freedom. Vaudemont makes the love declaration to her. He asks the young lady to give the red rose to him as the sign of love. Lo! Iolanta is picking up the white rose. Count has learnt of Princess' blindness. He describes the surrounding world and miraculous light to his lady, but it doesn't evoke any willing to be cured in her.
Desperate King Rene declares that if the surgery is failed, Vaudemont shall be punished. Endeavouring to save her beloved, Iolanta is ready to undergo any tortures and pangs. Ibn-Hakia takes her away.
Robert confesses to King Rene of his passion to Mathilde. He is set free of his promise. Bertrand conveys the wonderful news to everybody: Iolanta's sight is recovered. Vaudemont, Iolanta and King Ren? glorify the Light together with the other personages of the opera.