A Mach-Zehnder interferometer (MZI) coupled microring is demonstrated experimentally to obtain a high sensitivity as well as a large range for measuring change in refractive index. For the present MZI-coupled microring, there is a major resonance wavelength with a high extinction ratio (16-36 dB) in a very large wavelength span. Consequently, a very large quasi-free spectral range (>120 nm) is achieved, which helps to obtain a large measurement range. The MZI-coupled microring sensor is used for measuring the change of the ambient refractive index ranging from 1.0 to 1.538, and the sensitivity is as high as 111 nm/refractive index unit.