In this article, the conceptions of variability held by samples of Japanese and Thai senior high school mathematics teachers were identified, based on the framework proposed by Shaughnessy (2007), using a comparative survey study. From contrasting the results of the two groups, relative tendencies of insufficient statistical knowledge for variability were found in both samples, such as a tendency of Japanese teachers to overgeneralize equiprobability, whereas Thai teachers tended to overgeneralize estimation. Based on these findings, the use of well-known tasks from the research literature for this comparative study seems useful to clarify the relative tendencies and insufficiencies in teacher knowledge and conceptions regarding variability held by both groups.