On three other seats, where counting is underway, BJP is leading in two while Congress is ahead on one.
"Congress candidates have been declared elected in Deesa and Mangrol seats," Additional Chief Electoral officer A H Manek said.
"BJP candidates have been declared elected in Maninagar, Tankara, Talaja and Matar," Manek said.
Maninagar was the seat on which Prime Minister Narendra Modi emerged victorious thrice as a MLA.
On remaining three seats, Congress is leading in Khambhalia, while BJP is leading in Limkheda and Anand seats.
The by-polls are also considered as the litmus test of new Gujarat Chief Minister Anandiben Patel's leadership.
The BJP had sought votes in the name of Modi and Patel has asked voters to gift 10 seats to him ahead of his 64th birthday. Modi will reach Ahmedabad this evening and will be present here on his birthday tomorrow.