The quantum of punishment will be pronounced on Oct 3.
Yadav will face three to seven years' imprisonment.
"Lalu Prasad has been convicted in one of the cases - RC 20 A/96. He will be given four or more then four years of jail term," CBI lawyer Arvind Kumar Singh told reporters.
With this conviction, Yadav will now lose his Lok Sabha membership.
"As per a recent Supreme Court judgement a legislator convicted in a case where the minimum sentence is two years in jail will lose his/her seat immediately," said CNN-IBN.
On Sept 17, the court had reserved its verdict.
The Supreme Court on Aug 13 dismissed the plea of Yadav to transfer his trial in the case to another judge.
The apex court on Aug 6 reserved its verdict on Yadav in connection with the case.
On July 23, giving a relief to Yadav, the Supreme Court said it is willing to transfer one of the cases connected to the fodder scam to another judge.
Yadav had earlier alleged that the trial judge was a relative of a minister in the Bihar government.
Pertinently, the government is headed by Yadav's rival Nitish Kumar of the Janata Dal-United (JD-U).
The Supreme Court on July 9 restrained a Jharkhand court from delivering its judgement in connection with the scam.
The Jharkhand High Court on July 1 dismissed two petitions filed by Yadav in connection with the matter.
In his first plea, Yadav sought to transfer one of his fodder scam cases to another special CBI court from the present court one.
In another petition, he sought examination of one more witness.
On Mar 1, 2012, a CBI court framed charges against the RJD supremo and former Bihar Chief Minister Jagannath Mishra in connection with the scam.
The court also framed charges against Janata Dal-United MP Jagdish Sharma and former RJD MP RK Rana.
The case deals with the deceitful withdrawals of around Rs 46 lakh from Banka and Bhagalpur treasuries through fake enforced bills by the officials of state animal husbandry department between 1994-96.
The scam was revealed in Bihar in 1996.
Yadav served as Bihar Chief Minister at that time.
--IBNS (Posted on 30-09-2013)