From 2000 to 2005, we made several scientific expeditions to determine the ixodid tick fauna of the Brazilian state of Rondônia. Ticks were collected from vegetation, from wild and domestic animal hosts, and from humans. A total of 7,441 ixodid ticks were collected, representing 6 genera and the following 22 species: Ixodes fuscipes Koch, 1844, Ixodes luciae Sénevet, 1940, Amblyomma cajennense (Fabricius, 1787), Amblyomma calcaratum Neumann, 1899, Amblyomma coelebs Neumann, 1899, Amblyomma humerale Koch, 1844, Amblyomma incisum Neumann, 1906, Amblyomma latepunctatum Tonelli-Rondelli, 1939, Amblyomma longirostre (Koch, 1844), Amblyomma naponense (Packard, 1869), Amblyomma nodosum Neumann, 1899, Amblyomma oblongoguttatum Koch, 1844, Amblyomma ovale Koch, 1844, Amblyomma pacae Aragão, 1911, Amblyomma rotundatum Koch, 1844, Amblyomma scalpturatum Neumann, 1906, Amblyomma tigrinum Koch, 1844, Amblyomma varium Koch, 1844, Haemaphysalis juxtakochi Cooley, 1946, Dermacentor nitens Neumann, 1897, Boophilus microplus (Canestrini, 1887), and Rhipicephalus sanguineus (Latreille, 1806). We report for the first time the following tick species from the state of Rondônia: I. fuscipes, I. luciae, A. calcaratum, A. nodosum, A. pacae, A. tigrinum, D. nitens, B. microplus, and R. sanguineus. Except for B. microplus, D. nitens, and R. sanguineus, all tick species found in the present study were from areas of typical Amazon forest, which is still very abundant in many parts of the state. A few Amblyomma spp. were also found in a savanna habitat in the southern part of the state. Human infestations were mostly due to adult A. ovale and A. oblongoguttatum and immature Amblyomma spp.