The occurrence of Blastocystis sp. in cattle is reported herein for the first time in Spain. Stool samples from 554 bovines ranging from 3 days old to adults collected from 30 cattle farms in Aragón (northeastern Spain) were concentrated by the formalin-ethyl acetate method and examined light microscopically for the presence of gastrointestinal parasites. Vacuolated cells of Blastocystis sp. was detected in fecal specimens from 10 calves (1.8%) aged from 7 weeks to 6 months. Infected calves were detected at 3 of the 30 farms surveyed (10%). Blastocystis sp. cells were rounded or oval, with a diameter ranging from 6.25 to 15 microns. Blastocystis infection in cattle was never correlated with diarrhea, although infection intensities were generally low.