Peppermint essential oil (EO) has been extensively tested to date in reducing stored-product insects and insects of public health concern with very promising results, while only a few studies target important crop pests. There is also very little information on the effects of peppermint EO on non-target organisms, especially concerning contact and gastric effects at the same time. The goal of the investigation was the determination of the effect of peppermint EO on the mortality ofAphis fabaeScop.; the feeding intensity and weight gain ofLeptinotarsa decemlineataSay. larvae; and the mortality and voracity of non-target organismHarmonia axyridisPallas larvae. Our research indicates promising use for theM. piperitaEO against aphids and young larvae (second instars) of the Colorado potato beetle.M. piperitaEO showed good insecticidal efficacy againstA. fabaewith LC50= 0.5442% for nymphs and 0.3768% for wingless females after 6 h. Over time, the LC50value decreased. For the second instar larvae ofL. decemlineata, the LC50values were 0.6278%, 0.3449%, and 0.2020% after 1, 2, and 3 days of the experiment, respectively. On the other hand, older larvae (fourth instar) were characterized by significant resistance to the tested oil concentrations with LC50value = 0.7289% after 96 h.M. piperitaoil (contact and gastric effects) at a concentration of 0.5% was found to be toxic to young larvae (2 and 5 days old) ofH. axyridis, while EO at a concentration of 1% was toxic to 8-day-old larvae. Thus, for the sake of ladybug safety, it would be advisable to use EO fromM. piperitaagainst aphids at concentrations lower than 0.5%.