By employing sanguinarine, a natural active quaternary isoquinoline alkaloid, as a model molecule, a series of structurally simple quaternary 2-aryl-3,4-dihydroisoquinolin-2-ium compounds were designed and synthesized and evaluated for in vitro acaricidal activity against P. cuniculi. A new approach towards the title compounds was developed with isochroman as starting material. The results showed that 22 of 24 tested compounds displayed the activity in varying degrees at 0.4 mg/mL. Fourteen compounds were significantly more effective than ivermectin, a standard acaricide, and 6-methoxy dihydrosanguinarine, a derivative of sanguinarine (p<0.05). And their comprehensive relative activity was 1.4 to 16.5 times than that of ivermectin and 1.5 to 18.8 times than that of 6-methoxy dihydrosanguinarine. The structure-activity relationship indicated that the introduction of a substituent to N-benzene ring, especially halogen atom and trifluoromethyl group, led to great improvement of the activity. The position of fluorine atom, methyl group and hydroxyl group made very significant effects on the activity. It was concluded that 2-aryl-3,4-dihydroisoquinolin-2-iums are very promising candidates for the development of new isoquinoline acaricidal agents.Key words acaricidal activity; Psoroptes cuniculi; 2-aryl-3,4-dihydroisoquinolin-2-ium; 6-methoxy dihydrosanguinarine; sanguinarine; structure-activity relationship Acariasis is a chronic skin disease caused by mites, an ectoparasite, and widely occurs in animals and human. Psoroptes cuniculi is one of animal mites and mainly infects rabbits, goats, horses and sheep.1) It causes intense pruritus of animals with the formation of crusts and scabs and reduction of weight gain, or even death of animals.2,3) Therefore, this mite species causes serious economic losses for animal industry.Therapy and control of both human scabies and animal mange are based mainly on the use of effective drugs and chemicals. At present, the use of drugs to control these parasitic arthropods presents several problems including drugresistance 4,5) and environmental damage. 6,7) Ivermectin (Fig. 1), a clinically used acaricide, is increasingly being used to treat human scabies but often treatment failures, recrudescence and reinfection can occur.8) Concern over toxicity of many acaricides limits their use and reduces the number of Regular Article * To whom correspondence should be addressed. e-mail: zhoulechem@yahoo.com.cn; miaofangmf@163.com The authors declare no conflict of interest. # These authors contributed equally to this work.