Gutman proposed a topological index called the Sombor index, which was defined as
SO(G)=∑uv∈E(G)√(dG(u))2+(dG(v))2,SO(G)=∑uv∈E(G)√(dG(u))2+(dG(v))2,
where dG(v) is the degree of the vertex v in graph G. In this paper, we determine the second-minimum and second-maximum values of the Sombor index over all the unicyclic graphs of order n(n≥5) and bicyclic graphs of order n(n≥6).