BJP, which had won six out of the 10 seats in 2010, suffered a setback as it bagged just three seats. It was ahead in Hajipur constituency.
Of the seven results declared so far in the August 21 bye-election, RJD of Lalu Prasad has won Rajnagar (SC) and Mohiuddinnagar, according to Election Office.
JD(U) has won Jale seat while alliance partner Congress registered victory in Bhagalpur.
BJP has won Narkatiaganj, Banka and Mohania (SC) seats.
In the rest three seats, RJD is way ahead in Chapra, JD(U) is nearing victory at Parbatta and BJP is leading in Hajipur, the Election office said.
BJP had won six of the 10 seats in 2010 while RJD had three and JD(U) one.
The bypoll touted as "semi final" before crucial Assembly election next year was an acid test for the "secular alliance" comprising RJD, JD(U) and Congress to counter the BJP which won 31 of the 40 Lok Sabha seats with allies LJP and RLSP recentlly.
The bypoll on August 21 in the state had saw a low voting percentage of about 47.