Drp1, a dynamin-related protein, is essential for mitochondrial division in mammalian cells. Mutations in Drp1 cause mitochondria to form perinuclear clusters, indicating a shift toward mitochondrial fusion. Immunofluorescence and subcellular fractionation show that Drp1 is localized to mitochondria, suggesting a role in division. Time-lapse imaging of transfected cells shows Drp1 concentrates at sites of mitochondrial division. Purified Drp1 self-assembles into ring-like structures similar to dynamin, suggesting it wraps around mitochondrial constrictions. These findings support Drp1's role in mitochondrial division, similar to its function in yeast and C. elegans. Drp1's role in mitochondrial division was further confirmed by examining mutant Drp1. Temperature-sensitive mutations in Drp1 caused mitochondrial clustering, indicating a defect in division. Nocodazole treatment dispersed these clusters, revealing underlying defects. Drp1 mutant cells showed varied mitochondrial morphologies, including interconnected networks and collapsed structures, consistent with a block in division. Drp1 was found to be partly cytosolic and partly localized to mitochondria, consistent with its cycling between these compartments. GFP::Drp1 fusion protein localized to sites of mitochondrial division, with spots coinciding with division events. Time-lapse imaging showed Drp1 spots preceding division, supporting a direct role in division. Drp1 can form ring-like structures in vitro, similar to dynamin, suggesting it wraps around mitochondrial constrictions. These findings indicate Drp1 contributes to mitochondrial division in mammalian cells. Drp1's role in mitochondrial division is supported by its localization to division sites and its ability to form ring-like structures. While some studies suggested Drp1 might be involved in vesicular transport or ER-mitochondria fusion, these functions were not confirmed. Drp1's localization to mitochondria and its role in division are consistent with its function in yeast and C. elegans. Drp1's ability to form ring-like structures and its localization to division sites support its role in mitochondrial division.Drp1, a dynamin-related protein, is essential for mitochondrial division in mammalian cells. Mutations in Drp1 cause mitochondria to form perinuclear clusters, indicating a shift toward mitochondrial fusion. Immunofluorescence and subcellular fractionation show that Drp1 is localized to mitochondria, suggesting a role in division. Time-lapse imaging of transfected cells shows Drp1 concentrates at sites of mitochondrial division. Purified Drp1 self-assembles into ring-like structures similar to dynamin, suggesting it wraps around mitochondrial constrictions. These findings support Drp1's role in mitochondrial division, similar to its function in yeast and C. elegans. Drp1's role in mitochondrial division was further confirmed by examining mutant Drp1. Temperature-sensitive mutations in Drp1 caused mitochondrial clustering, indicating a defect in division. Nocodazole treatment dispersed these clusters, revealing underlying defects. Drp1 mutant cells showed varied mitochondrial morphologies, including interconnected networks and collapsed structures, consistent with a block in division. Drp1 was found to be partly cytosolic and partly localized to mitochondria, consistent with its cycling between these compartments. GFP::Drp1 fusion protein localized to sites of mitochondrial division, with spots coinciding with division events. Time-lapse imaging showed Drp1 spots preceding division, supporting a direct role in division. Drp1 can form ring-like structures in vitro, similar to dynamin, suggesting it wraps around mitochondrial constrictions. These findings indicate Drp1 contributes to mitochondrial division in mammalian cells. Drp1's role in mitochondrial division is supported by its localization to division sites and its ability to form ring-like structures. While some studies suggested Drp1 might be involved in vesicular transport or ER-mitochondria fusion, these functions were not confirmed. Drp1's localization to mitochondria and its role in division are consistent with its function in yeast and C. elegans. Drp1's ability to form ring-like structures and its localization to division sites support its role in mitochondrial division.