Abstract: In the context of the light trading in China’s carbon trading pilot markets, this paper employs the methods of variance ratio test to carry out a weak form efficiency test on the five carbon trading pilot markets in Shenzhen, Beijing, Shanghai, Guangdong and Hubei. The findings show that if the light trading characteristics in the markets are not taken into consideration and if the daily data checking is adopted, then only Shanghai carbon trading market presents a lower weak-form efficiency, the rest markets are not weak-form efficient. When weekly data is used for testing, it is found that the carbon trading markets in Hubei and Guangdong present weak-form efficiency, the Shenzhen market is not sure, while the markets in Beijing and Shanghai present weak-form inefficiency. When the data obtained during the active trading period is used for testing, it is found that all the five pilot markets have reached weak-form efficiency by different degrees, especially since entering 2016. This indicates that China’s carbon trading pilot markets are on the way to become mature.

Key words: thin market; carbon trading market; weak form efficiency; variance ratio test