Seven UV absorbers of benzotriazol structure were prepared by diazotisation, coupling, reduction and alkylation. The phase transfer catalyst (PTC) triethylbenzyl ammonium chloride (TEBA) was used in alkylation. Their structures were characterized by IR, NMR, MS and elementary analysis. The UV visible absorption of those UV absorbers was also tested. The increase of their molar absorption coefficient and the red shift of their wavelenghth were due to the chlorine in their molecule structures.