The bypoll results are being viewed as crucial in the countdown to the Assembly polls in Uttar Pradesh next year.
The ruling party's candidate Anand Sen Yadav won Bikapur constituency in Faizabad district securing 68,896 votes and defeating his nearest RLD rival Munna Singh Chauhan by a margin of 62,456 votes, a release issued by Election Office here said.
Congress candidate Mavia Ali has won Deoband (Saharanpur) seat defeating his nearest rival Meena Singh by a margin of 3,559 votes.
In Muzaffarnagar seat, BJP's Kapil Dev Agarwal defeated his nearest SP rival Gaurav Swarup Bansal by margin of 7,352 votes.
While the BJP candidate got 65,378 votes, the SP nominee polled 58026 votes.
The by-elections were necessitated in Muzaffarnagar, Deoband and Bikapur due to death of SP MLAs Chitranjan Swaroop, Rajendra Singh Rana and Mitrasen Yadav last year.