Al-Malik as-Salih Najm al-Din Ayyub (died November 1249) was the Ayyubid ruler of Egypt from 1240 to 1249.

In 1221 he became a hostage at the end of the Fifth Crusade, while John of Brienne became a hostage of as-Salih's father Al-Kamil, until Damietta was reconstructed and restored to Egypt. In 1232 he was given Hisn Khayfa in the Jazirah (northern Iraq), which his father had captured from the Ortoqids. In 1234 his father sent him to rule Damascus, removing him from the succession in Egypt after suspecting him of conspiring against him with the Mamluks. His uncle as-Salih Ismail soon expelled him from Damascus, and he fled to the Jazirah, where he allied with the Khwarezmians.

In 1238 al-Kamil died and was succeeded by his son Al-Adil Abu Bakr , as-Salih's brother; by 1240 as-Salih had overthrown him and taken control of Egypt. In 1244 the Khwarezmians sacked Jerusalem, which had been handed over to Frederick II, Holy Roman Emperor by al-Kamil during the Sixth Crusade. Later that year as-Salih and the Khwarezmians defeated as-Salih's uncle in Syria, who had allied with the crusader Kingdom of Jerusalem, at the Battle of La Forbie . In 1245 as-Salih captured Damascus, and was awarded the title of sultan by the caliph al-Musta'sim in Baghdad. The next year the combined forces of the Ayyubids defeated the unruly Khwarezmians, who no longer recognized as-Salih as their lord.

In 1249 Louis IX of France invaded Egypt on the Seventh Crusade, and occupied Damietta. As-Salih was away fighting his uncle in Syria, but quickly returned and encamped at al-Mansourah, where he died of disease in November. As-Salih's heir, al-Muazzam Turanshah , was far away in the Jezirah, and his widow, Shajar al-Durr, hid his death until Turanshah arrived. Nevertheless, the Mamluks, whom as-Salih had mostly recruited from the Kipchak Turks, gained power in Egypt, and were ultimately responsible for defeating the crusade. Their dynasty, the Bahri dynasty, were named after their barracks on an island in the Nile (Bahr al-Nil). The Bahriyya were also called Salihiyya, after as-Salih. The Mamluks did not control Syria, however, and as-Salih was the last Ayyubid to rule a united territory.