The quantum controlled-not gate is an example of the maximally entangling gate, which is a broad class of operations that are necessary for scalable linear optics quantum computation. Here, we characterize a telecommunications-wavelength (1550 nm) quantum controlled- not gate, and for the first time, experimentally bound its process fidelity by measuring its operation in two complementary polarization bases. The gate's final process fidelity F is given by 91% ?? F ?? 95%.