JD(U) will now have 128 members, six more than the magic figure of 122.
The 13 MLAs, including five Muslims, met at the residence of party MLA Samrat Chaudhary and wrote to Speaker Uday Narayan Chaudhary withdrawing allegiance from the RJD and expressing support to the Nitish Kumar government, MLA Javed Iqbal Ansari told PTI.
Assembly Secretary Phool Jha confirmed to PTI receipt of a letter from the 13 RJD members informing the Speaker about leaving their party.
Samrat Chaudhary, son of senior RJD leader Shakuni Chaudhary, who flew with the chief minister in a helicopter to Khagaria yesterday to inaugurate a road bridge said, "It will be better for Prasad to merge the party with Congress instead of allying with it for the Lok Sabha elections.
"The party which sent him to jail by tearing up an ordinance has become the ideal of Prasad who is losing no opportunity to pester its leaders," he told reporters.