A miniature Fabry Perot (F-P) optical fiber humidity sensor based on agar film is proposed.The sensor forms a double F-P structure by inserting a standard single-mode optic al fiber into an empty core glass tube and dipping agar film on the end face of the glass tube.When the ambient relative h umidity changes,the volume and refractive index of agar film change,resulting in wavelength shift of interfere nce light.The humidity sensing experimental system is built to characterize the humidity sensing characteristic s of the sensor.The relative humidity measurement sensitivity of up to 1.2324nm/% RH is realized i n the relative humidity range of 50%RH—80%RH.The sensor has the advantages of compact size,low cost,good linear sensitivity and simple preparation method.