Echinostomiasis is a food-borne intestinal, snail-mediated parasitosis caused principally by ingestion of snails infected with digenean trematodes of the Echinostoma genus. The treatment and control of trematodiasis is usually done by administration of praziquantel (PZQ). In this study, we evaluated the effect on Echinostoma paraensei of different doses of praziquantel through analysis of morphological parameters using light microscopy, scanning electron microscopy, and confocal scanning laser microscopy along with parasitological data. We used 30 female mice aged 4 weeks. Each animal was given 40 metacercarie of E. paraensei by gavage. The animals were divided into five groups, each group containing six animals, where one group was utilized as untreated control. Two weeks after infection, the mice were given praziquantel by gavage at total dosages of 12.5, 25, 50 or 100 mg/kg by body weight. Two days after treatment, the mice were euthanized in a CO(2) chamber for recovery of helminths in the small intestine. The doses of 50 and 100 mg/kg of praziquantel eliminated all the worms. There were significant differences (p<0.05) between all the treated groups when compared to the control group. The body morphology showed contraction with vacuolization of the parenchyma, and the spine of the peristomic collar was not evident by light microscopy. The scanning electron microscopy revealed that the other doses caused retraction of spines of the peristomic collar and also the tegument spines at the body edge, as well as the development of vesicles and peeling; all these alterations were more evident at the dose of 25 mg/kg. In turn, the confocal scanning laser microscopy revealed vacuolization and disorganization of spines and vitelline glands. E. paraensei responds differently to experimental treatment with praziquantel according to the doses utilized causing morphological alteration and even worm elimination.