Let F be a field and q(x) a quadratic polynomial in F[x] with q(0)≠0. We denote by T∞(F) the algebra of all infinite upper triangular matrices over the field F. A matrix A∈T∞(F) is called a quadratic matrix with respect to q(x) if q(A)=0. In this paper, we first investigate the subgroup in T∞(F) generated by all quadratic matrices with respect to q(x) and then present some applications.