Organelles play essential roles in cellular homeostasis and various cellular functions in eukaryotic cells. The current experimental strategy to modulate organelle functions is limited due to the dynamic nature and subcellular distribution of organelles in live cells. Optogenetics utilizes photoactivatable proteins to enable dynamic control of molecular activities through visible light. This modality has been rapidly expanded for the dynamic regulation of organelle functions. This chapter describes a method by optical modulation of the mitochondria-lysosome contacts (MLCs). Detailed procedures of transfection, optogenetic MLCs, mitochondrial morphology, and functional analysis are described. Optogenetic control of organelles in live cells offers an innovative paradigm for cell engineering and synthetic biology.