A total of 4,575 ticks were collected from 5,953 small mammals captured from March 2004 to December 2008 at 19 military training areas and 6 US military installations, Gyeonggi and Gangwon Provinces, Republic of Korea. Ixodes nipponensis (98.9%; 753 nymphs, 3,771 larvae) was the most frequently collected tick, found on six of the 11 small mammal species captured, followed by Ixodes pomerantzevi (1.1%; 17 females, 9 nymphs, 24 larvae) found on two species. While only one T. sibiricus was collected, it was infested with 44 ticks, with an infestation rate of 100.0%, followed by Rattus norvegicus (16.7%, n=18), Apodemus agrarius (14.6%, n=5,397), Crocidura lasiura (7.5%, n=265), Microtus fortis (7.3%, n=82), Myodes regulus (5.7%, n=53), and Micromys minutus (4.8%, n=63). No ticks were collected from Apodemus peninsulae (n=3), Mus musculus (n=58), Tscherskia triton (n=12), and Mogera wogura (n=1). Ixodes nipponensis nymphs were most frequently collected from small mammals from March to April, while larvae were more frequently collected during September. Ixodes pomerantzevi was collected only during February–April 2008, and a single Haemaphysalis flava nymph was collected from A. agrarius in August 2004.