An image quality compensation device for an organic light emitting display includes: a memory having first and second update blocks selectively storing first and second period compensation values, which are sequentially updated at regular intervals; and a timing controller that configures the first update block as either the current memory page for data loading or the next memory page for data writing and the second update block as the other one of the two, based on a preset check code, and updates the memory by calculating the second period compensation value with the passage of driving time based on the first period compensation value loaded from the update block configured as the current memory page, writing the second period compensation value to the update block configured as the next memory page, and then erasing the first period compensation value from the update block configured as the current memory page.