The resistance distance between any two vertices of a graph le="Click to view the MathML source">G is defined as the network effective resistance between them if each edge of le="Click to view the MathML source">G is replaced by a unit resistor. The Kirchhoff index le="Click to view the MathML source">K(G) is the sum of the resistance distances between all the pairs of vertices in le="Click to view the MathML source">G. A bicyclic graph is a connected graph whose number of edges is exactly one more than its number of vertices. In this paper, we completely characterize the bicyclic graphs of order le="Click to view the MathML source">n≥4 with minimal Kirchhoff index and determine bounds on the Kirchhoff index of bicyclic graphs. This improves and extends some earlier results.