Tetranychus urticae Koch (Acari: Tetranychidae) is an economically important pest of agricultural and ornamental crops worldwide. It has been shown that many of natural plant-based pesticides have fewer side effects compared with synthetic chemicals. The essential oils of plants have been broadly studied for pest-control, including toxic and repellent effects, antifeedant, ovicidal, and other properties. Essential oils from stems, flowers, and leaves of Piper marginatum Jacq. were evaluated in the laboratory regarding their acaricidal potential against the two-spotted spider mite (T. urticae) and the results were compared with eugenol as a positive control. The oils were also evaluated with regard to the susceptibility of the natural enemy of T. urticae (Neoseiulus californicus McGregor). Based on LC50 estimates, oils from stems and flowers exhibited the same toxicity and differed significantly from the leaf oil with LC50 0.37, 0.56, and 3.77 μL L-1, respectively. None of the oils tested exhibited toxicity greater than or equal to that of the positive control. The oil mortality rate was significantly lower for N. californicus (50% to 70%) than for T. urticae (> 95%). The P. marginatum oils also deterred oviposition. Among the chemical constituents tested, sesquiterpenes were more toxic with an LC50 of 2.89 μL L-1 than phenylpropanoids Z-asarone and E-asarone with LC50 6.64 and 8.51 μL L-1, respectively. The acaricidal properties, oviposition deterrence and selectivity make these oils strong candidates for use as the active ingredient in a plant-based acaricidal agent.