All-trans retinoic acid (ATRA) was firstly used as a differentiating agent in 1987 in Shanghai for the treatment of acute promyelocytic leukemia (APL). Retinoic Acid Syndrome (RAS) became an important complication of therapy after the administration of ATRA. The frequency of syndrome is 27% and the precise cause is not entirely known. The mortality rate of patients with APL due to this complication is 1%. Symptoms of RAS resembles to sepsis, pneumonia, iatrogenic volume overload and blood transfusion reactions frequently seen in the course of leukemia and may cause confusion in the diagnosis of RAS. Dexamethasone must be administered urgently in the suspicion of RAS since it has a fatal outcome. Herein, we reported an APL patient with white blood cell count of lower than 1000/ml at presentation and complicated with retinoic acid syndrome subsequent to the first dose of all-trans retinoic acid.