Semen was collected from five of each of young (3-5 years) and old (6-10 years) Friesian bulls and extended with tris-yolk fructose extender (1 semen: 20 extender). The extended semen was cooled to 5ºC over 2 hours, then frozen in straws. After 24 hours, the frozen semen was thawed and supplemented with caffeine at levels of 0 and 10 mM/100 ml. Frozen-thawed semen with caffeine was then incubated at 37ºC for 4 hours. The percentages of post-thawing motility, freezability and acrosome status of spermatozoa, were estimated. Conception rates for the thawed-semen frozen in each of young and old bulls, were also assessed.                 The results showed that, freezing of the young bull semen maintained (P< 0.01) higher the percentages of post-thawing motility and freezability than old bull spermatozoa. Supplementation of caffeine at a level of 10 mM to the thawed-frozen semen in each of young or old bull significantly (P< 0.01) higher the percentages of post-thawing motility and freezability of spermatozoa, during thawing-incubation at 37ºC for up to 4 hours. The incubation time had a significant (P<0.01) effect on decreasing the percentages of post-thawing motility and freezability of young and old bull spermatozoa. The percentages of live spermatozoa with intact acrosome decreased (P<0.01) and the percentages of dead spermatozoa with intact acrosome increased (P<0.01), however, the percentages of live and dead spermatozoa with detached acrosomes showed decreased significantly (P<0.01) with the successive time of incubation. The percentages of live spermatozoa with each of intact or detached acrosomes in young were insignificantly higher than old bulls. However, the percentages of dead spermatozoa with each of intact or detached acrosomes in young were significantly (P<0.01) lower than old bulls. Supplementation of caffeine at a level of 10 mM to the thawed-frozen semen showed insignificant higher the percentage of live spermatozoa with intact or detached acrosomes and significantly(P<0.01) lower the percentages of dead spermatozoa with intact or detached acrosomes than free-caffeine medium.                 Conception rates for cows artificially inseminated with the thawed-frozen semen were insignificantly higher in young than old bulls.