In order to investigate the electrostatic charging tendency (ECT) of transformer oil under thermal aging and understand its correlations to the other insulation parameters, a series of accelerated aging tests were carried out on two types of mineral insulation oils, A and B, both of which were mainly used in 500 kV power transformers in China. Oil samples were pre-processed by degassing and dehydrating, and then aged at 120°C for various periods up till to 675 h, meanwhile, different contents of oxygen and copper/pressboard/silicon steel sheet were also added into the oil samples for sensitive study. The results indicate that the ECT of oil A increases notably with aging time, the ECT of oil B however does not change so much during the whole aging period. Injection of oxygen in the samples enhances the ECT of oil A, such a promotion effect is minor for oil B. The correlations between the ECT and other parameters, such as tanδ, volume resistivity (ρ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</sub> ) and acid number were analyzed as well. There are linear correlations between ECT and tanδ, acid number and log (ρ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</sub> ) of oil A, of which ECT and tanδ has the highest correlation coefficient of 0.881. Regarding oil B, there is only a positive linear correlation between ECT and acid number.