Sanjay Singh, who is also JD-U spokesperson, filed the defamation case against the former Bihar chief minister in the Patna civil court.
"I have filed a case against Lalu Prasad," Sanjay Singh told IANS.
Lalu Prasad had allegedly described Sanjay Singh and another JD-U leader Sanjay Jha as "alsatian" at his Parivartan Rally in the Bihar capital last week.
The RJD chief had launched a scathing attack against Chief Minister Nitish Kumar for rampant corruption, bribery and rising incidents of rape in the state and said he would throw him out of power in the next elections.
"People of the state are looking for a change (parivartan) and the RJD will oust Nitish Kumar from power," Lalu Prasad had said.