Phat si-io (also transliterated as pad see ew or pad si u, Thai: ผัดซีอิ๊ว, pronounced [pʰàt sīːʔíw] or [pʰàt sīʔíw] is a Chinese-influenced stir fried noodle dish that is commonly eaten in Thailand. It is also quite popular in Thai 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 kuai-tiao 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.
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.