An in-fiber Mach-Zehnder interferometer humidity sensor based on waist-enlarged fiber tapers cascade structure was proposed and demonstrated.The sensor head is formed by a taper-single-mode-taper-single-mode-taper structure through arc fusion splicing.The change of the humidity and temperature will make the optical path difference changed of the sensor core mode and cladding modes, causing interference spectral change.Through monitoring the spectra variation can determine the ambient physical quantities.The experimental results show that the humidity sensitivity of the sensor is -0.065 dB/%RH with a linearity of 0.997 in the humidity range of 35-95%RH;the temperature sensitivity of the sensor is 69.4 pm/℃ with a linearity of 0.998 in the temperature range of 30-80 ℃.This sensor can avoid the cross-sensitivity to humidity and temperature, make it a good candidate for high accuracy humidity and temperature applications.