Cyclocondensation of a series of substituted phenoxy methylene carboxylic acids with thiosemoicarbazides afforded 2-Amino-5-Aryloxy Methylene -1,3,4 Thiadiazoles (Ia-Ie). The later were subsequently condensed with different phenoxymethylene carboxylic acid chlorides into 2- Aryloxy Methyleneamido-5-Aryloxy Methylene-1,3,4-Thiadiazoloyl Amides. The wood preservation efficiency of the both class of compounds was evaluated against a wood rotting fungus Gleophyllum Straitum at different concentrations using food poison technique. In general phenoxy derivatives have shown more control over the growth of Gleophyllum Straitum than their corresponding aminothiadiazoles at 500 ppm. The chlorophenoxy-substituted thiadiazoles among all have shown more activity then others against Gleophyllum Straitum.