Bimetallic nanoparticles are synthesized using two different metal elements and used recently in many fields. However, limited studies related to the ecotoxic effects of nanoparticles available in the literature. The purpose of this study is to synthesize and characterize bimetallic PdCu/MWCNT and PdNi/MWCNT NPs and investigate their ecotoxic effects on earthworms. For this purpose, we injected approximately 20 mu L of various concentrations of bimetallic PdCu/MWCNT and PdNi/MWCNT NPs (1, 10, 100, 1000, and 2000 mg/L) into the coelomic space of earthworms. We evaluated survival rate, malformations, reactive oxygen species (ROS) level, 8-OHdG content, and histopathological changes in earthworms at the 48th hour after exposure. PdCu/MWCNT and PdNi/MWCNT NPs were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) pattern, and Raman-scattering spectroscopy. Toxicological examinations showed that PdCu/MWCNT NPs reduced the survival rate of earthworms (2000 mg/L, 84%) and caused various malformations (various lesions, thinning, swelling, and rupture), but nonsignificant effects of survival rate and malformations were observed in earthworms using PdNi/MWCNT NPs. The histopathological examinations of earthworm tissues exposed with PdNi/MWCNT determined that tissues in all treatment groups had a normal histological appearance. However, at a concentration of 2000 mg/L of PdCu/MWCNT NPs, atrophy in the longitudinal muscle layer and less degenerative cells in the epidermis layer were observed in earthworm tissues. It was determined that PdNi/MWCNT and PdCu/MWCNT NPs caused significant increases in ROS levels and 8-OHdG activity in earthworm tissues after 48 h. Finally, our results demonstrated that the toxicity of PdNi/MWCNT NPs was detected to be lower than PdCu/MWCNT NPs. However, both nanoparticles may pose a toxicological risk at high concentrations (1000 and 2000 mg/L). These findings will provide valuable information to studies on the use of PdNi/MWCNT NPs in wastewater treatment systems, industrial and medical fields, which have been determined to have less ecotoxicological risk.