In this paper, we obtain the following main theorem for a free quadratic bialgebra J:(a) For p≠0, J is a pointed cosemisimple coalgebra. For p=0, J is a hyperalgebra.(b) For p≠0 and q≠0, J has antipode S iff p·q+2=0 and S(x)=x. Forp=0 or q=0, J hasantipode and S(x)=-x.(c) All left J*-modules are rational.Also, we give some applications in homological theory and algebraic K-theory.