The oustings were the latest sign that Zhou Yongkang, once a member of the Politburo Standing Committee (PSC), China's most powerful body, is being targeted.
His fall would send shockwaves through China's political establishment. PSC members have generally been regarded as untouchable even after retirement.
Ji Wenlin, formerly a vice governor of the southern island of Hainan and before that a secretary to Zhou, was stripped of his party membership, the Central Commission for Discipline and Inspection (CCDI), the party's internal watchdog, said in a statement.
Zhou used to head the CPLC, which oversees the public security ministry. Overseas Chinese reports claimed Ji, Yu and Tan were all his secretaries.
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All three took advantage of their posts and "accepted huge amounts of bribes by seeking gains for others", the CCDI said, adding that their cases have been transferred to judicial authorities for criminal prosecution.
Yu and Ji were also accused of adultery, according to the statements.
Xu, who was until 2012 a member of the Communist Party's elite 25-strong Politburo, is the first of its former members to fall in the current crackdown on graft, which follows the ascension of Xi Jinping to power as the head of the party.
A number of officials and others with close ties to Zhou have come under investigation in recent months, and the former security chief himself is now at the centre of rumours about a corruption probe.
Analysts say this week's expulsions are a strong signal that authorities are set to make an announcement regarding Zhou.