Reactions of azide-alkilic cycloaddition are well known since 1893. At the same time, with the elaboration of click chemistry, the techniques of labelling biological objects, particularly by fluorescent dyes, were widely developed. The use of fluorescent labels provides the ability to visually monitor the process streamlines hardware load and reduces research time. Fluorescein is among the fluorophores mostly used for labelling of biomolecules due to its high quantum yields and good stability in biological media. However, despite of commercial availability of fluorescein derivatives functionalized for use in click reactions, methods for their synthesis are virtually absent in the literature. Therefore, we have developed a reliable and effective methodic for the synthesis of functionalized fluoresceines for the use in the click reactions. Synthesis of diacetyl N-(4-azidobutyl)-fluoresceine-5(6)-carboxamide was performed in six stages, starting form resorcinol and trimellitic acid anhydride. The diacetylated analogue was synthesized for the click modifications in the “soft” conditions, since N-(4-azidobutyl)-fluorescein-5(6)-carboxamide is poorly soluble in the classic organic solvents. Proposed synthetic protocol allows to increase the yield of the final and intermediate compounds and to optimized the procedure of their isolation and purification.