The aim of the campaign is to "expose the failure" of Chief Minister Jitan Ram Manjhi in the state and the achievements of the Narendra Modi government at the centre, BJP leaders said.
"It is part of our preparation for the 2015 assembly elections. We have to galvanise our workers and reach out to as many people as possible," BJP's chief spokesperson Vinod Narayan Jha said.
The party chose Sep 25 to launch the campaign as it coincided with the beginning of Navratri, one of the biggest Hindu festivals.
The day also marked the birth anniversary of Bharatiya Jana Sangh leader Deen Dayal Upadhyaya.
Jha told IANS that the BJP will organise meetings in all the 8,463 panchayats and 2,900 urban wards as well as other places till Oct 15.
Around 25 lakh leaflets in Hindi would be distributed among people, with at least 10,000 leaflets in each of the 243 assembly constituencies.
The leaflets will highlight the 100-day performance and achievements of the Narendra Modi government, and the likely return of "jungle-raj" following the recent alliance of the JD-U, RJD and the Congress.
Former deputy chief minister Sushil Kumar Modi Thursday addressed a public meeting at Hajipur while Leader of Opposition in the assembly Nand Kishore Yadav spoke at Muzaffarpur and the BJP state chief Mangal Pandey at Purnia, BJP legislator Sanjay Mayukh said.Many central government ministers and parliamentarians would address meetings at various places across the state.
In the recent byelections, the RJD won three seats, the JD-U two, while the Congress wrested the Bhagalpur seat from the BJP after 23 years.