Abstract: Present work is a continuation of our previous research done in the field of transformation reaction of isothiuronium salts derived from various lactones and lactames giving substituted 2-iminothiazolidin-4-ones or 2-aminothiazolin-4-ones. These compounds are known e.g. for their significant biological activity but they do not possess any fluorescence behaviour. On the other hand some substituted 1,3-thiazol-4-oles are good fluorophores in solutions and sometimes also in solid state. It is also known that the presence of some ionizable groups (OH, NH2 etc.) can significantly affect the shift of their UV absorption/fluorescence band. Therefore we have prepared a new set of substituted 5-(2-hydroxyphenyl)-1,3-thiazol-4-oles and studied their spectral properties under various conditions.