Between 1996 and 2013, 71 blue-crowned laughingthrush (Dryonastes courtoisi) chicks, a small passerine bird endemic to China, were born at Mulhouse Zoo in northeast France. None of them survived past 1 yr, and 82% died between 0 and 6 days old of an unidentified cause and despite an attempt to establish an artificial breeding protocol. Atoxoplasma spp., causing a disease known as systemic isosporosis, is a coccidian parasite that can infect several species of birds. Mulhouse's adult birds were suspected to be infected with Atoxoplasma spp. and to transmit this parasite to their offspring. A treatment with toltrazuril (Baycox® 2.5%) was implemented in the four adult birds. Coprologic examinations were performed before, during, and after the treatment to quantify the parasite load in feces. Polymerase chain reaction (PCR) assays were used to test blood samples from the adult and liver, lung, gizzard, and kidney samples from 10 chicks to detect Atoxoplasma spp. Five of the 10 chicks had some tissue samples positive for Atoxoplasma spp. in at least one of the three repeats of the atoxoplasmosis PCR. An average of 181 Isospora spp. oocysts per gram of feces were found in the group of adults before treatment. This number was reduced to zero 1 wk after the beginning of the toltrazuril treatment. The PCR results suggest a transovarian transmission of Atoxoplasma spp., but further investigation is needed for confirmation. The treatment with toltrazuril appears to allow a significant reduction of the parasite excretion.