Increased galectin-3 expression has been currently showed to be associated with poor prognosis in some hematological malignancies, such as acute myeloid leukemia, diffuse large B cell lymphoma. However, little is known about the clinical significance of galectin-3 in patients with acute promyelocytic leukemia (APL). We investigated the concentration of serum galectin-3 and characterized the relationship between galectin-3 and outcome in patients with APL. Higher galectin-3 levels were detected in patients with APL compared with the healthy controls (p < 0.001). Higher galectin-3 levels were closely associated with older ages (p < 0.001), the medical history of psoriasis (p = 0.036), coagulopathy (p = 0.042), and CD34 expression (p = 0.004). Compared with patients with lower galectin-3 levels, those with higher galectin-3 levels had significant shorter overall survival (p = 0.028) and relapse-free survival (p = 0.001). Multivariate analysis showed that serum galectin-3 was an independent unfavorable factor for relapse-free survival in patients with APL treated with all-trans retinoic acid and arsenic trioxide-based frontline therapy. Clinical impact of galectin-3 should be further investigated in patients with APL.