Carvacrol is a monoterpenoid phenol present in the oils of various plants including Origanum vulgare (oregano) or Origanum majorana (marjoram). For a long time, it has been used as spice in foods because of its antimicrobial properties. Additionally, it appears to have anticancer effects against some cancer but this has not been well studied. Therefore, we conducted various assays to confirm the effects of carvacrol on choriocarcinoma cell lines (JAR and JEG3). Our results indicate that carvacrol has antiproliferative properties and induces apoptosis, resulting in increased expression of proapoptotic proteins. Additionally, carvacrol disrupted the mitochondrial membrane potential and induced calcium ion overload in the mitochondrial matrix in both JAR and JEG3 cells. Furthermore, carvacrol generated oxidative stress and lipid peroxidation in both JAR and JEG3 cells. Moreover, carvacrol-suppressed phosphoinositide 3-kinase-protein kinase B and extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase (MAPK) signal transduction whereas expression of phosphor-P38 and c-Jun N-terminal kinase MAPK was increased. Together, our results indicate that carvacrol may be a possible new therapeutic agent or supplement for the control of human choriocarcinomas.