Expelled JDU leader Shyam Rajak joined RJD on August 17.
Rajak joined RJD in presence of Tejashwi Yadav in Patna.
This comes a day after Bihar Chief Minister Nitish Kumar sacked Rajak as State Industries Minister.
CM Kumar also expelled him from JDU.
Slamming Bihar Chief Minister, Rajak said almost all ministers are unhappy with Nitish Kumar.
"Almost all ministers in JDU are unhappy with Nitish Kumar.
Currently, the ministers are unable to make a decision," he said.
"I, however, don't have any idea about who's going to leave the party.
I am joining RJD, that is all I can say," he added.
Earlier, Rajak challenged his expulsion, terming it 'illegal'.
He said he was going to Assembly Speaker to submit resignation as member.
Rajak was expelled for being allegedly involved in anti-party activities.
He was expelled just months before Bihar assembly polls.
Incidentally, Rajak had switched to JDU in 2009 after leaving RJD.
He had won from Phulwari seat as a JDU nominee in 2010 election.