Tau, known primarily as a microtubule-binding protein, is also found in the nucleus where it binds to DNA. Recent investigations have focused on its role in stabilizing DNA and chromosomes, but the biophysical understanding of its molecular mechanisms, particularly regarding tau’s phase separation properties, remains limited. In this study, we used in vitro single-molecule assays to show that tau interacts with DNA to form co-condensates, significantly altering the mechanical properties of DNA. Our findings indicate that tau can wet the DNA strand in low-salt conditions, effectively condensing and stiffening the DNA. At high concentrations, tau also forms droplet-shaped condensates on DNA, similar to its interaction with microtubules. Notably, these condensates are mobile and may act as nucleation sites for microtubule growth. This study reveals previously unknown effects of Tau-DNA condensation and suggests that these interactions could influence microtubule dynamics during mitosis.