To detect sub-ppm levels of HCl gas, spectral changes of tetraphenylporphine and derivatives dispersed in ethylcellulose were examined in the visible region. For free base tetraphenylporphyrin, the absorbance at 450 nm and 670 nm is sensitive to sub-ppm levels of HCl and also a good reversibilty is observed at room temperature. The Soret and Q-bands are insensitive to NH3, Cl-2, NO2 and NO at room temperature. For zinc tetrabromotetraphenylporphine, the absorbance at 479 nm and 722 nm is sensitive to sub-ppm levels of HCl gas and also good reversibilty is observed at room temperature.