The photocatalytic degradation of a herbicide derivative, glyphosate [(N-phosphonomethyl) glycine] has been investigated in aqueous suspensions of titanium dioxide at different pH values. This compound was found to degrade more efficiently under alkaline pH, where no adsorption takes place on the surface of the catalyst in the dark. The main degradation route involves the cleavage of the P-C bond giving rise to sarcosine and glycine as the intermediate products formed during the photooxidation process.