Pyrimidines, either mononuclear or condensed with other heterocycles have established its importance in medicinal chemistry. Variety of biological activities have been reported by thiazolo[4,5-d]pyrimidine derivatives. The present work describes the synthesis and antifungal activity of several 3-(substituted)-5-(substituted)phenylamino-6-(substituted)phenylthiazolo[4,5-d]pyrimidine-7(6H) -one-2(3H)-thiones. The target compounds were synthesized by cyclocondensation of 4-amino-5-carbethoxy-3-(substituted)thiazolo-2(3H)-thione and S-methyl di(substituted) phenylisothiourea. All synthesized compounds were tested for minimum inhibitory concentration against different fungal strains such as, Aspergillus niger, A. clavatus and Candida albicans and compared with fluconazole and nystatin as reference drug. Some of the compounds have exhibited potent inhibitory activity on all fungal strains, and were found more potent than reference standard. Some of the important structural features required for broad spectrum activity in this series have been derived.