Monkey embryonic stem (ES) cells are a useful tool for studying early human development and evaluating the efficacy of stem cell therapy. Monkey ES cells show closer similarity to human ES cells than their mouse counterparts regarding morphology, cell surface markers, and the maintenance of pluripotency, including the leukemia inhibitory factor requirement. The generation of genetically modified monkey ES cells with a biomarker such as green fluorescent protein, which allows noninvasive monitoring of progeny ES cells, is invaluable for the development of cell transplantation therapy and the study of differentiation mechanisms in primates. Here, we describe the generation of green fluorescent protein-expressing monkey ES cells using a conventional electroporation method.