Many smokers incorrectly believe that “light” cigarettes are less harmful than regular cigarettes. To address this problem, many countries have banned “light” or “mild” brand descriptors on cigarette packs. Our objective was to assess whether beliefs about “light” cigarettes changed following the 2007 removal of these brand descriptors in Thailand and, if a change occurred, the extent to which it differed by socioeconomic status. Data were from waves 2 (2006), 3 (2008), and 4 (2009) of the International Tobacco Control (ITC) Thailand Survey of adult smokers in Thailand. The results showed that, following the introduction of the ban, there was an overall decline in the two beliefs that “light” cigarettes are less harmful and smoother than regular cigarettes. The decline in the “less harmful” belief was considerably steeper in lower income and education groups. However, there was no evidence that the rate of decline in the “smoother” belief varied by income or education. Removing the “light” brand descriptor from cigarette packs should thus be viewed not only as a means to address the problem of smokers’ incorrect beliefs about “light” cigarettes, but also as a factor that can potentially reduce socioeconomic disparities in smoking-related misconceptions.