Ca²⁺-regulated photoproteins genetically fused with biospecific polipeptides have been extensively used in intracellular Ca²⁺ measurements and in the development of binding assays. Gene fusions to aequorin have been limited to its N-terminus, since as previous studies indicated the protein loses bioluminescent activity upon modification of its C-terminus. To investigate this in regard to another photoprotein – obelin (OL) the one was elongated at its C-terminus with tyrosine (Y) and then fused with green fluorescent protein Clytia gregaria (cgreGFP) through the flexible 31 aa linker. Both proteins (OL-Y and OL-cgreGFP) were isolated and investigated. The OL-Y was found to form a stable photoprotein comlex, possessing 75% of WT-OL bioluminescent activity. OL-cgreGFP activity preserves 46% of WT-OL activity and demonstrates an effective resonance energy transfer, where OL-partner and cgreGFP-partner are energy donor and acceptor respectively. Thus, it was shown that the labels on the base of Ca²⁺-regulated photoprotein obelin may be obtained by fusing with bio-specific polypeptides regardless its termini.