The deposition of tetrakis (4-sulonatophenyl) porphyrin (TPPS) thin film on optical fibers presents many possibilities for sensing applications.The J-form aggregation with a narrow and sharp spectral feature at about 490nm and its sensitivity to humidity have been discussed;a fast change of wavelength occurs according with variation in the humidity level.The reproducibility and high sensitivity of TPPS-coated fibers,along with the capabilities of optical fibers,suggest the device as a good candidate for humidity sensing in harsh environments.