The repellency and toxicity of a CO-derived cedarwood oil (CWO) was evaluated against actively questing unfed nymphs of four species of hard ticks: Amblyomma americanum (L.), Dermacentor variabilis (Say), Ixodes scapularis Say, and Rhipicephalus sanguineus (Latreille). Using a vertical climb bioassay for repellency, nymphs of these species avoided a CWO-treated filter paper in proportional responses to treatment concentrations. At 60 min of exposure, I. scapularis nymphs were most sensitive with 50% repellency concentration (RC) of 19.8 µg cm, compared with RC of 30.8, 83.8 and 89.6 µg cm for R. sanguineus, D. variabilis and A. americanum, respectively. Bioassays determined the lethal concentration for 50% (LC) and 90% (LC) mortality of nymphs exposed to CWO in treated vials after 24- and 48-h exposure. After 24 h exposure, the LC values were 1.25, 3.45 and 1.42 µg cm and LC values were 2.39, 7.59 and 4.14 µg cm for D. variabilis, I. scapularis and R. sanguineus, respectively, but had minimal effect on A. americanum. After 48 h exposure, the LC values were 4.14, 0.78, 0.79 and 0.52 µg cm, and LC values were 8.06, 1.48, 1.54 and 1.22 µg cm for A. americanum, D. variabilis, I. scapularis and R. sanguineus, respectively. The repellency of CWO on tick species decreased with time. The repellency and toxicity bioassays demonstrated concentration-dependent responses of tick nymphs to the oil, indicating the potential of the CO-derived cedarwood oil be developed as an eco-friendly repellent and/or acaricide.