The ZnS/polymer films have been successfully prepared by casting technique with different thickness (10,12,13.5 and 14 ) and to carry out a comprehensive study of their gas detection performance. All the different ZnS polymer films thickness demonstrates excellent selectivity and accuracy and stability. ZnS- doped PMMA films show higher sensitivity to ethanol vapors. Further, the films show fast response and recovery to methanol and methanol vapors at higher operating temperatures. The methanol-ethanol sensing mechanism of the film has been explained.