This study aimed to evaluate the use of a sodium alginate matrix-pelletized formulation of Duddingtonia flagrans for biological control of gastrointestinal nematodiasis in feedlot goats in the semiarid region of Northeastern Brazil. We used 20 Saanen female goats (age, 4 months; average weight, 12 kg) that did not receive anthelmintic treatment and had counting of eggs per gram of faeces (EPGs) ? 500. The animals were divided into two groups: in group 1 (D. flagrans group), each animal received 3 g of pellets (0.6 g of D. flagrans mycelium) per 10 kg of body weight, twice a week, over 4 months; and in group 2 (control group), each animal received 3 g of pellets without fungus per 10 kg of body weight, twice a week, over 4 months. Each group was maintained in a separate 15-m2 stall. Larval cultures and measurements of weight, EPG, and packed cell volume (PCV) were performed every 15 days. We observed low EPG levels in the D. flagrans group throughout the experimental period, with a significant difference (p < 0.05) on day 30 and from day 60, having, at the end of the experiment, average OPG values of only 150, reduction of 92.3% when compared to control group. Haemonchus sp. was the most prevalent helminth in all larval cultures. The D. flagrans group showed a mean weight gain of 8.8 kg at the end of the experiment (p < 0.05), while the control group showed a mean weight gain of 4.8 kg. The best PCV results (p < 0.05) were also observed in the D. flagrans group from day 30. Thus, the use of D. flagrans pellets in a sodium alginate matrix was effective in controlling gastrointestinal nematodiasis of feedlot goats in the semiarid region of Northeastern Brazil.