Abstract:A unicyclic graph is either a cycle or a cycle with trees attached. GUO Jiming gave the first largest Laplacian spectral radius among all unicyclic graphs with cycle length g and n vertices. In this paper,the first largest [g/2]graphs is determined according to Laplacian spectral radii among all unicyclic graphs with cycle length g and n=g+k(g≥5,k≥3) vertices.