The study aimed to evaluate the efficacy of fenbendazole and piperazine citrate against ascariasis in naturally infected calves of Sylhet government dairy farm, Sylhet, Bangladesh. The study included 84 calves of which 40 were naturally infected. Twenty calves of 1-8 month old were selected on the basis of body weight and faecal egg counts irrespective of sex infested with ascariasis for this experiment and were randomly divided into four equal groups (group A, B, C and D) where each group consisted of 5 calves and calves of group D were kept as control. Two fenbendazole (7.5 mg kg-1 body weight, orally) and piperazine citrate (220 mg kg-1 body weight, orally) preparations were used for treatment of ascariasis in group A, B and C, respectively. Before trials (day 0), total egg count, blood samples and initial body weight were recorded. During the study the fecal and blood samples were collected directly from the rectum and jugular vein, respectively on 7th, 14th, 21st and 28th day. Fecal samples were examined using McMaster fecal egg counting method. Body weights were recorded on day 0 and day 28 following the treatments. The comparative efficacies of different anthelmintic of two fenbendazole were 95.50% and 95.58%, followed by piperazine citrate 97.27%, respectively. McMaster fecal egg counting method discloses the percentage of prevalence of ascariasis 35.71% (1-2 months), 24.00% (3-4 months), 21.74% (5-6 months) and 18.18% (7-8 months), respectively. After treatment with two fenbendazole and piperazine citrate, total erythrocyte count (TEC), hemoglobin (Hb) content and packed cell volume (PCV) increased significantly (p<0.01) in calves but erythrocyte sedimentation rate (ESR) and total leukocyte count (TLC) decreased significantly (p<0.05) in all treated calves. Body weight increased significantly (p<0.01) on day 28. Results of the present study revealed the efficacy of multiple anthelmintic against gastrointestinal nematodes in calves. Further studies are required to understand the efficacy of the anthelmintics widely used in different agro-ecologies and livestock industry in Bangladesh.