Repellent and acaricidal activities of eucalyptus oil, permethrin, and DEET against Leptotrombidium pallidum larvae, which are a vector transmitting tsutsugamushi disease, were evaluated under laboratory conditions using a filter paper impregnated method. The LD₅₀ values of eucalyptus oil and DEET were 0.025 and 0.018 ㎎/㎠, respectively while that of permethrin was higher than 0.2 ㎎/㎠. In the repellency test of these materials at 6.14 ㎎/㎠, eucalyptus oil gave complete repellency, and the larvae crossed the treated zone killed. But permethrin showed 60% repellency at 9.20 ㎎/㎠ and the mites croosed the zone were not killed. The percent repellency of DEET at 0.53 ㎎/㎠ was 8.3 and 2.8 times higher than that of permethrin and eucalyptus oil, respectively. The acaricidal activities of emulsifiable concentrates-pump sprayers containing the eucalyptus oil as an active ingredient were assayed. The emulsifiable concentrates containing 1% and 3% eucalyptus oil showed weak mortality at 1 hour after treatment, while all ones containing more than 6% oil produced 100% activity against L. pallidum larvae. The mortality also increased as exposure time to the concentrates increase. These results suggest that the potential of eucalyptus oil highly expected to be used as a control or repellent agent against L. pallidum larvae may be very high.