Kumar came to the party office in the morning and after doing yoga and taking bath there, began the fast. State JD(U) President Basistha Narayan Singh, senior minister Vijay Chaudhary, Shyam Rajak, Rajiv Ranjan Singh Lallan, JD(U) MPs Ali Anwar, Harbansh, Gulam Rasool Balyawi and senior party leader Sanjay Jha joined Kumar in the protest.
Scores of other party leaders and workers also sat on the protest fast in the party office premises.
JD(U) MPs, MLAs and office bearers are observing similar fast across the state against the Bill.
In a brief speech, Bihar JD(U) President said Kumar and other party leaders were protesting Centre's Land Acquisition Bill in Gandhian style.
The satyagraha is aimed at stirring the heart of the people sitting in power at the Centre "who are out to take away the living of almost three-fourth population of the country for whom agriculture is the source of livelihood," Singh said.
He described the Land bill introduced in Parliament by Prime Minister Narendra Modi government as "anti-farmer" and "pro-corporate" and said the party would continue to agitate against it till it is withdrawn.
Gandhian bhajan was played during the satyagraha.
Kumar had earlier protested against the land acquisition Bill introduced by Prime Minister Narendra Modi government in Parliament by terming it a 'black law' and demanded its immediate recall.
"The Bill seems to have taken the heart out of the legislation prepared in 2013 by the UPA government," he had said and declared Bihar would not implement it "at any cost".
Kumar had also supported the agitation of social worker Anna Hazare over the Bill recently in Delhi.