The optical properties of many microporous zeolite crystals, e.g. refractive index and Raman spectra, change dramatically upon adsorbing and desorbing molecules in the zeolitic pores. Such adsorption-induced changes in optical properties of zeolites can be used for chemical sensing with high sensitivity. Recently, a new type of zeolite thin film-fiber integrated microsensors has been developed in our lab for highly sensitive chemical detections in gas and liquid phases. In this presentation, the sensor fabrication technique and the optical sensing mechanisms will be explained in detail. Application of these microsensors for studying the molecular transport in zeolite membranes/thin films will be particularly discussed with experimental results on a number of organic molecules, which are of great interests to zeolite membranes separations.