It is not known when Du Xiao was born. Both his grandfather
Du Shenquan and father
Du Rangneng served as
chancellors during
Tang dynasty — Du Shenquen during the reign of
Emperor Yizong, and Du Rangneng during the reigns of Emperor Yizong's sons
Emperor Xizong and
Emperor Zhaozong. Du Rangneng was a close confidant of Emperor Zhaozong's. In 893, after Emperor Zhaozong's failed campaign against the warlords
Wang Xingyu the military governor of Jingnan Circuit (靜難, headquartered in modern
Xianyang,
Shaanxi) and
Li Maozhen the military governor of Fengxiang Circuit (鳳翔, headquartered in modern
Baoji,
Shaanxi) — a campaign that Du Rangneng had coordinated after Emperor Zhaozong ordered him to even though he was against the campaign — Wang and Li marched on the imperial capital
Chang'an; under duress from them, Emperor Zhaozong was forced to order Du Rangneng to commit suicide. After Du Rangneng's death, Du Xiao mourned him bitterly, and even after the traditional three-year mourning period, he still partially wore mourning clothes for over a decade and did not embark on an official career. His older brother Du Guang'ai () was suffering from a mental illness, such that at times he would act out violently or speak angrily, but despite this, Du Xiao served him humbly as an older brother. During Emperor Zhaozong's
Guanghua era (898-901), when the chancellor
Cui Yin served also as the director of salt and iron monopolies, Cui offered him a number of positions in the imperial government — as an assistant to Cui as the director of the monopolies; as a
Xiaoshulang (), a copyeditor at the
Palace Library; a county sheriff near Chang'an; and a scholar at Hongwen Pavilion (); he declined them all. Later, after Emperor Zhaozong was forced by the warlord
Zhu Quanzhong the military governor of Xuanwu Circuit (宣武, headquartered in modern
Kaifeng,
Henan) to move to
Luoyang, the chancellor
Cui Yuan, who was then also serving as the director of taxation, offered him the posts of assistant to Cui as director of taxation and the deputy director of palace affairs (殿中丞,
Dianzhong Cheng). Cui spoke to him to persuade him to accept: Du lost his position as imperial scholar and was only serving as
Shanbu Yuanwailang. Several months later, however, he was given the responsibility of drafting imperial edicts, and was then given back his position as imperial scholar, and promoted to a supervisory position as
Shanbu Langzhong (). == During Later Liang ==