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 optical fiber into an empty core glass tube and dipping agar film on the end face of the glass tube.When the ambient relative humidity changes,the volume and refractive index of agar film change,resulting in wavelength shift of interference light.The humidity sensing experimental system is built to characterize the humidity sensing characteristics of the sensor.The relative humidity measurement sensitivity of up to 1.232 4 nm/% RH is realized in 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.