A total of 2,235 ticks were collected from 2,505 small mammals, representing nine mammal species in eight genera, captured from January to December 2009 in the Republic of Korea (ROK). Survey sites includedNightmare Range, a ROK-operated military training area, and Camp Humphreys, a US Army installation, in Gyeonggi Province. Apodemus agrarius (1,998, 79.8%) was the most frequently captured small mammal, followed by Microtus fortis (212, 8.5%), Crocidura lasiura (159, 6.3%), Myodes regulus (54, 2.2%), Mus musculus (49, 2.0%), Micromys minutus (26, 1.0%), Rattus norvegicus (3, 0.1%), Apodemus peninsulae (2, 0.08%), and Tamias sibiricus (2, 0.08%). While A. agrarius accounted for 91.1% of all small mammals at Nightmare Range, it only accounted for 68.0% at Camp Humphreys. Ixodes nipponensis (99.5%; 1,977 larvae, 247 nymphs) was the most frequently collected tick, having been found on 6/9 (66.7%) of the small mammal species, followed by Haemaphysalis flava (0.5%; 10 larvae, 1 nymph) from 3/9 (33.3%) species of small mammals. Overall, the highest infestation rate was observed for T. sibiricus (50.0%, 1/2), followed by A. agrarius (18.1%, 360/1,998), M. minutus (11.5%, 3/26), C. lasiura (4.4%, 7/159), M. fortis (3.8%, 8/212), M. musculus (2.0%, 1/49), and M. regulus (1.9%, 1/54). No ticks were collected from A. peninsulae (n=2) or R. norvegicus (n=3). Although similar numbers of small mammals were collected at Nightmare Range (1,272) and Camp Humphreys (1,233), the tick infestation rate was nearly four times higher at Nightmare Range (23.4%) compared to Camp Humphreys (6.7%). Ixodes nipponensis nymphs were first observed and peaked in April, followed by declining numbers through September/October. Low numbers of larvae were first observed in April and continued through June. Relatively large numbers of larvae were collected from July to September, resulting in higher than average infestation rates during the same period.