A vertex-degree-based molecular structure descriptor was introduced by Ivan Gutman, named the Sombor index. The Sombor index of a graph \(G\) is defined as \(SO(G)=\sum\limits_{uv\in E(G)} \sqrt{d_{G}(u)^{2}+d_{G}(v)^{2}}\), where \(d_{G}(u)\) denotes the degree of the vertex \(u\) in \(G\). In this paper we determine the extremal values of Sombor index of tricyclic graphs.