Sze Yup, Sze Yap, Seiyap or Si Yi are the four counties of Xinhui, Taishan, Kaiping and Enping in the Pearl River Delta, in southern Guangdong Province, China. Today these are four of the five county-level cities of the administered from the city of Jiangmen .
The area gave rise to the of Cantonese. Although Sze Yup and Standard Cantonese are both dialects of , they are mutually unintelligible. Therefore Sze Yup emigrants have kept their identity, even among other Cantonese emigrants.
In the 19th century, many people from Sze Yup emigrated to Hong Kong, Southeast Asia, Australasia, North America and South America. The Punti-Hakka Clan Wars also erupted in these counties during this time.