A humidity sensor based on microfiber Bragg grating is proposed and demonstrated.The microfiber Bragg grating is obtained through chemical etching commercial fiber Bragg grating.The experimental results show that the central wavelength of the microfiber Bragg grating has red shift with humidity increasing,while the power decreases.The relative humidity sensitivity of the microfiber Bragg grating with diameter of 4.45um is 3pm/%RH in the range of 55%-80%RH.Furthermore,the sensor has a linear response to humidity with linear fitting of 0.991.The sensor possesses advantages of easy fabrication and low cost.