Neurofibrillary tangles of hyperphosphorylated tau are a fundamental hallmark of Alzheimer’s disease. In this study, we investigate the behavior and impact of mutant tau with MTBD deletion is unable to bind to microtubules. Through use of DNA from mice and molecular cloning, we create plasmids with WT and mutant tau DNA that can then be expressed in COS-7 cells to study the behavior and effect of mutant tau in COS-7 cells, especially with regards to the microtubule network. Immunostaining of COS-7 cells expressing the mutant GFP-tau gene depicts inability to bind to microtubules, aggregate formation, and diffused masses within the cell. We conclude that if these mutant tau proteins were to be in a cell that has microtubules reliant on tau for stability, the mutant tau would negatively affect the dynamic instability of microtubules. To investigate the effect of mutant tau proteins on cell viability, drug treatments that negatively affect the dynamic instability of microtubules were used as a unit test to mirror the effect of mutant tau proteins. The results display that microtubules lacking dynamic instability cause cell death. Through the tests conducted in this study, we conclude that mutant tau in neurons would likely cause neurodegeneration.