Summary: U(1) Chern-Simons theory is quantized canonically on manifolds of the form \(M = \mathbb{R}\times \Sigma\), where \(\Sigma\) is a closed orientable surface. In particular, we investigate the role of the mapping class group of \(\Sigma\) in the process of quantization. We show that, by requiring the quantum states to form representation of the holonomy group and the large gauge transformation group, both of which are deformed by quantum effect, the mapping class group can be consistently represented, provided the Chern-Simons parameter \(k\) satisfies an interesting quantization condition. The representations of all the discrete groups are unique, up to an arbitrary sub-representation of the mapping class group. Also, we find a \(k \leftrightarrow 1/k\) duality of the representations.