"I have decided to quit the BJP to protest inadequate representation to the Kushwaha Samaj during ticket distribution for the general elections," the 83-year-old leader, who was earlier with the Congress, told reporters here.
Amid speculations that he might join the JD(U), Singh, however, refused to divulge anything.
Singh, who had served as the state chief minister for five days, between January 28 to February 1, 1968, had joined the BJP on September 22 last year after spending a long time in wilderness.