Mitochondrial genetic diseases are complex disorders that impair cellular energy production, leading to diverse clinical manifestations across multiple organ systems. These diseases arise from mutations in either mitochondrial DNA or nuclear DNA. Among nuclear DNA-related cases, mutations in POLG and POLG2, which encode subunits of mitochondrial DNA polymerase γ, are particularly significant, causing conditions such as Alpers-Huttenlocher syndrome and progressive external ophthalmoplegia. Model organisms have been instrumental in elucidating POLG-related disease mechanisms and advancing therapeutic strategies. Saccharomyces cerevisiae (budding yeast) provided insights into fundamental mitochondrial functions, while Caenorhabditis elegans (roundworm) helped explore POLG's roles in multicellular organisms. Drosophila melanogaster (fruit fly) has been pivotal in studying neurological aspects, and Mus musculus (mouse) models contributed to understanding systemic effects in mammals. Recently, Danio rerio (zebrafish) has emerged as a promising vertebrate model for drug screening, due to its optical transparency and genetic tractability. Each model system offers unique advantages, collectively bridging the gap between basic research and clinical applications. This review will examine in vivo models used in POLG disorder research, highlighting their contributions to understanding disease mechanisms and therapeutic advancements.