Cài (Simplifie and Traditional Chinese: 蔡) is a Chinese surname that derives from the name of the ancient Cai state. It's regionally more common in China's Fujian Province and in countries settled by ethnic Chinese from that province than in China as a whole. The surname is the 34th most common surname in China, but the 9th most common in Taiwan, where it is usually romanized as Tsai, and the 8th most common in Singapore, where it is usually romanized as Chua.