Emperor Jin Xiaowudi 晉孝武帝 (r. 372-396), personal name Sima Yao 司馬曜, courtesy name Changming 昌明, was one of the last emperors of the Jin dynasty. He was the third son of Emperor Jianwen 晉簡文帝 (r. 371-372), his mother was Ms Li 李氏. Sima Yao was first Prince of Guiji 會稽 and in 372 obtained the title of Heir Apparent (huang taizi 皇太子). In the same year, he succeeded his father to the throne, at the age of just ten sui. The main consort of his late father therefore, Empress Dowager Chu 褚太后, took over regency. Policy was carried out following the advice of Xie An 謝安 (320-385), who held the position of Vice Director of the Imperial Secretariat (shangshu puye 尚書仆射). In 373, a new reign motto was chosen – Ningkang 寧康 "Peace and Strength". Two years later, a Ms Wang 王 was made main consort of the young emperor.
Sima Yao held his first court audience in 376. At that occasion, he paid homage at the tombs of his ancestors and chose a new reign motto, Taiyuan 太元 "Great Origin". The government decided to abolished the field tax, which was calculated according to the size of the field. Instead, a poll tax (see household tax system) of 3 hu 斛 (see weights and measures) per person was introduced. Persons serving in corvée (yaoyi 徭役) were freed from tax payment for the current year.
The most important event for the Jin empire occurred in 383, when the ruler of the Former Qin empire 前秦 (351-394), Fu Jian 苻堅 (r. 356-384), fielded an army of "a million" troops towards the south. In the battle of River Fei 淝水 (close to present-day Shouxian 壽縣, Anhui), the invader was defeated. This stalemate cemented the division between northern and southern China for the coming 200 years.
Sima Yao was a Buddhist and had built a prayer hall (jingshe 精舍) inside the imperial palace, and invited monks to reside there. This step contributed to the spread of Buddhism in south China. On the other hand, Sima Yao was known as a drunkard and was often unable to fulfil his duties as a ruler.
After Xie An's death in 385, Sima Yao made his younger brother Sima Daozi 司馬道子 (364-403), the Prince of Langya 琅琊, regent of the Jin empire. Daozi was arrogant, covetous, and envious, and made himself quite a few enemies. He raised taxes and fought against eventual opponents. The regent was only reined somewhat after 390, when the emperor's brother-in-law, Wang Gong 王恭 (d. 398), was appointed Director of the Imperial Secretariat (shangshu ling 中書令) and regional inspector (cishi 刺史) of the provinces of Yanzhou 兗州 and Qingzhou 青州. One measure to control Sima Daozi better was his transfer to the princedom of Guiji 會稽 in the southeast.
In 396 the emperor began to order a series of construction work and had built the Hall of Purifiying the Heat (Qingshu Dian 清暑殿) and the Palace of Everlasting Peace (Yong'an Gong 永安宮). In the same year he fell ill and died. He was buried in Mound Longping 隆平陵 and was given the posthumous title Xiaowu 孝武 "Filial-Martial".
He was succeeded by his son Sima Dezong 司馬德宗, known as Emperor An 晉安帝 (r. 396-418).