Programmed cell death or apoptosis is regulated process of cell suicide. The central role in apoptosis play cysteine proteases called caspases. Caspases recognize tetra-peptide sequences Asp-Glu-Val-Asp (DEVD) on their substrates and hydrolyze peptide bonds after aspartic acid residues. Various techniques for the determination of caspase-3 are commercially available e.g. Enzyme Linked Immuno-Sorbent Assay (ELISA), Western blotting or flow cytometric analysis. The products of the cleavage can be detected by spectrophotometry, fluorimetry, chemiluminescence (CL) or ELISA. In this work, we suggested fluorescent sensor based on Förster Resonance Energy Transfer (FRET) to determine caspase-3 in cell nucleus or cytoplasm by apoptosis for very fast analysis by fluorescence microscopy without sample destroying.