Amyotrophic lateral sclerosis (ALS) involves progressive degeneration of motor neurons, resulting in muscle weakness and ultimately death. Mutations in the SPTLC1 and SPTLC2 genes, essential subunits of serine palmitoyltransferase, are linked to early-onset ALS. They disrupt the homeostatic inhibition of SPT. However, the mechanisms of how excess sphingolipid synthesis leads to cellular and organelle dysfunction and ultimately neurodegeneration remain unclear. SPT localizes to the ER-mitochondria contact sites. Furthermore, a rise in mitochondrial sphingolipid content has been linked to mitochondrial bioenergetics dysfunction and activation of apoptotic pathways. Our study investigates how excessive sphingolipid production affects mitochondrial function in cell models of SPT-related ALS. We find that SPT-related ALS patient fibroblasts and iPSC-derived motor neurons recapitulate the increased de novo sphingolipid biosynthesis we previously described systemically in patients and cell transfections. Our sphingolipidomic study on mitochondrial isolates confirmed elevated levels of sphingolipids, including ceramides in mitochondria from SPT-related ALS fibroblasts. These SPT-related ALS cell models also show decreased mitochondrial respiration which was restored upon SPT inhibition by D-cycloserine. Accompanying these bioenergetic defects were mitochondrial morphological changes including mitochondrial swelling, and accumulation of neuronal processes in iPSC-derived motor neurons and patient fibroblasts in comparison to controls. These studies provide a mechanistic link between excessive sphingolipids synthesis and mitochondrial dysfunction and identify SPT inhibition as a plausible therapeutic approach for SPT-related ALS. In future studies we will compare transcriptomic gene expression profiles between patient and control fibroblasts to identify and interrogate mitochondrial and other cellular pathways that may be disrupted in this disease.