Standard Thai tones are divided into two categories; namely, level tones (mid tone, low tone, and high tone) and contour tones (falling tone and rising tone). 

The Thai high tone was found to have changed its height and shape between the years 1911 and 2006 (Bradley 1911; Abramson 1962; Tumtavitikul 1992; Morén and Zsiga 2006). The tone changed its shape from mid falling (1911) to high level (1962), and then to mid rising (2006). 

This study attempts to show that the high tone in Standard Thai is changing its phonetic characteristics from high level to mid rising. The informants were divided into two age groups: over-sixty and under-twenty. Each age group was comprised of twenty informants. The Praat program was used to conduct an acoustic analysis. The results show that the high tone shape in the over-sixty group is high level, but it is mid rising in the under-twenty group. It has also been found that the present characteristic of the high tone is similar to that of the rising tone. It is argued whether the Standard Thai high tone should be categorized as a contour tone. Standard Thai high tone variations indicate the plausibility of observing an ongoing change. In addition, some ongoing change in the falling tone is also discussed.