Abstract This study evaluated the prevalence and seasonality of natural infection by gastrointestinal parasites and the susceptibility of different dairy buffalo categories in Bandeirantes, state of Mato Grosso do Sul, Brazil. Forty-one Murrah buffaloes were divided into three categories, 11 suckling calves (0-8 months old), 10 weaned calves (8-18 months old), and 20 adult females over the age of 18 months. Adult animals were free from parasitism or showed very low parasite load. The suckling calves showed a peak of egg per gram of feces (EPG = 2038) in November, when the average rainfall was 69.3 mm and the temperature 25.95 ºC, while the lowest egg count (167) occurred in May, two months after the peak of 234.68 mm and 20.59 ºC. Weaned calves showed two peaks of EPG from 1288.89 and 875 in September and June, with rainfall of 41.45 and 18.4 mm, temperature 24.16 and 20.69 ºC, respectively. Significant (p = 0.01) and negative (r = -0.33) correlation between the EPG of suckling calves and precipitation was observed. The most common gastrointestinal parasites were Haemonchus sp. and Cooperia sp.