Abstract : Paraoxonase 1 (PON 1) is an enzyme synthesized in the liver and is associated with high density lipoprotein (HDL) in the systemic circulation. It is an antioxidant in which prevents oxidative stress and inflammation. Since oxidative stress had been proven to be the complication of hyperthyroidism due to increase metabolic rate, this study is trying to look for the association between PON1 activities and phenotype in untreated hyperthyroid Malay patients. A total of 107 Malays subjects consisting of 55 untreated hyperthyroid patients (TSH<0.01 mU/L) and 52 healthy subjects were included.. The phenotype of the serum was determined by using the ratio of salt stimulation PON 1 activity to the arylesterase activity. The median difference of basal PON 1 activities level between untreated hyperthyroid compared to the healthy control was not statistically significant (p=0.23). There is no correlation between PON 1 activity and TSH (r=0.18, p=0.899) and free T4 (p=0.130). The most common PON 1 phenotype was AB followed by BB and then AA phenotype in Malay population. There is no significant correlation between free T4 and TSH with PON 1 activity in untreated hyperthyroid hence, PON 1 activity is not affected by thyroid status. AB is the most common phenotype in Malay population followed by BB phenotype in Malay population in Kelantan.