Inclusion Criteria:  Mild or moderate-to-severe GO according European Group on Graves' orbitopathy (EUGOGO) guidelines diagnosed by endocrinologist and ophthalmologist. Three categories of participants are included:  Mild GO Active moderate-to-severe GO with contraindication to glucocorticoid Inactive moderate-to-severe GO No previous treatment of GO except for eyedrops Euthyroidism (normalized free T4 and TSH) for at least 2 months. If radioactive iodine is used for hyperthyroidism, euthyroidism needs to be achieved for at least 6 months.  Exclusion Criteria:  Sight-threatening GO according to EUGOGO guidelines diagnosed by endocrinologist and ophthalmologist. Pregnancy Drug or alcohol abuse Unable to comply with the study protocol Unable to obtain informed consent Use of hydroxychloroquine or systemic steroid within 3 months prior to enrollment History of side effects of hydroxychloroquine History of retinopathy Renal dysfunction (estimated glomerular filtration rate (eGFR) < 60ml/min) Hepatic dysfunction (aspartate aminotransferase (AST) or alanine aminotransferase (ALT) > 2 x upper limit) Anemia (hemoglobin (Hb) < 10g/dl) Neutropenia (absolute neutrophil count < 100/uL) Thrombocytopenia (platelet (PLT) < 150000/uL) Glucose-6-phosphate dehydrogenase (G6PD) deficiency Porphyria cutaneous tarda Allergy to 4-aminoquinoline