Nearly all Chinese surnames are one character; a small number are two, such as 欧阳, 司马, 诸葛 and 上官. Famous bearers include 司马迁 and 诸葛亮. In pinyin the whole surname is one word: Sīmǎ Qiān, never Sī Mǎqiān.
usage
Less often, 复姓 is a verb: to take back one's original surname, for example after being adopted into another family.
