Phat si io (also written as pad see ew or pad si u, Thai: ผัดซีอิ๊ว, RTGS: phat si-io, pronounced [pʰàt sīːʔíw] or [pʰàt siʔíw]; Lao ຜັດສີອິ໊ວ) is a Chinese-influenced stir fried noodle dish that is commonly eaten in Laos and Thailand. It is also quite popular in Thai and Lao restaurants around the world.
The name of the dish translates to "fried (with) soy sauce" and it is very similar to the char kway teow of Singapore and Malaysia. Phat si io is normally stir fried dry while another similar dish, rat na (in Thai) or lard na (in Laos), is served in a thickened sauce and generally has a lighter taste.
Phat si io is made with dark soy sauce ("si-io dam"), light soy sauce ("si-io khao"), garlic, broad rice noodles, called kuaitiao sen yai in Thai (commonly abbreviated to just sen yai meaning "big strip"), Chinese broccoli, egg, and some form of thinly sliced meat — commonly pork, chicken or beef — or shrimp or mixed seafood. The name comes from the soy sauce used in the dish, which in Thai is called "si-io", a loanword from Teochew. Phat si io is sometimes also called kuai-tiao phat si io, which reflects the general practice of using flat rice noodle as the main ingredient. However, other types of noodles may also be used.