During 1965–67, the seasonal history and habits of two oak bark beetles, Pseudopityophthorus minutissimus (Zimm.) and P. pruinosus (Eichhoff), were studied in 47 oaks, Quercus spp., in southern Ohio.All study trees were attacked and the male beetles made initial entry into the trees. The attack period per tree was usually 1–3 days, and the density of attack varied from 5 to 120 galleries 1 ft2 of surface area. Oviposition began as soon as egg gallery construction began, and the incubation period was about 5 days in the summer. The rate of egg gallery construction was about 0.2 in./day in mid-summer. The average length of the egg galleries was 1.9 cm and the average number of eggs per gallery was 41.5. Over 50% of the parent adults of both species re-emerged after egg gallery construction and oviposition. The re-emerging parent adults can attack, lay eggs, and re-emerge three times. The larval stage can last 25–247 days, the pupal stage 15–139 days, and the adult stage 7–198 days. The beetles can overwinter in every stage but the pupal stage. Spring emergence occurred 29 April in 1966 and 14 April in 1967, and in southern Ohio, two generations and a partial one occur each year.Trap trees were attacked 7–205 days and brood emergence lasted 58–329 days. The beetles can attack one tree three times.