Thick and thin film λ/2 microstrip L section rejection filters in the X and Ku bands have been used to investigate the effect of leaf moisture on their response. The results reported are in the form of a comparative study of the X and Ku band response of the rejection filters. The investigations are aimed at using the overlay technique for studying the effect of leaf moisture changes on the rejection property of the filter. The leaves investigated were Tradescantia (magenta), Pothas Scandens (green), and Acalypha (bicolored red and green). These leaves were chosen because of their differences in thickness, texture, and color or chlorophyll content. The effects in the Ku band are more dramatic than in the X band for high moisture content (fresh leaves). The results show differences in the response of the thick and thin film filters to condition of leaf overlay. The response to moisture content in the dried leaves is almost similar irrespective of type of metallization of the filter, though the thick film filter seems to be more useful in the X band since some differences between 24 hour dried and 48 hour dried leaf overlay are seen.