The prevalence and anthelmintic efficacy of Abamectin against gastrointestinal parasites under field conditions in Faisalabad (Punjab, Pakistan) was studied in 100 horses. The overall prevalence of gastrointestinal parasites was 75%, including Strongylus spp. (50%), Oxyuris equi (12%), Parascaris equorum (8%) and mixed infection (5%). Among these naturally infected animals, 15 were selected. These horses were assigned to three groups on the basis of prevalent species of gastrointestinal parasites. Each group had five animals, comprising four treatment horses and a control horse. Abamectin was evaluated against these gastrointestinal parasites with a single shot at the dose rate of 0.2 mg/kg body weight administered through subcutaneous route which resulted in 98% reduction in faecal egg count after day 14 post-treatment. Non-treated horses remained positive for gastrointestinal parasites. No adverse reactions were observed during the experimental period. It was concluded that Abamectin is highly effective against gastrointestinal parasites in horses.