Anatomical features of wood cells and their size variations are key elements of wood identification. This research focuses on the microscopic differentiation between four Quercus species, two Red Oaks (Q. cerris and Q. rubra) and two White Oaks (Q. alba and Q. petraea). More specifically, it studies the variation of vessels width in earlywood and latewood. The results showed that in earlywood, Q. rubra exhibited the widest vessels (332.27 ± 65.21 μm), followed by Q. cerris (300.27 ± 57.62 μm), Q. petraea (286.09 ± 58.83 μm), and Q. alba (200.82 ± 43.50 μm), in descending order of size. Conversely, in latewood, Q. cerris displayed the largest vessels (83.89 ± 20.31 μm), with Q. rubra following closely (74.05 ± 20.31 μm). Q. petraea (35.34 ± 6.11 μm) and Q. alba (26.70 μm) maintained their order, appearing a consistent pattern between the wood growth phases. The variability in vessel dimensions was also supported by statistical differences among most species combinations both in earlywood and latewood. The investigation of certain vessel traits may serve as a valuable component of studies related to wood properties and species adaptability in the context of climate change.