1. Molecular formula: B1a C48H74O14 B1b C47H72O14 2. Formula Weight: B1a: 874 B1b: 860 3. Description: Light yellow or white crystalline powder, Solublein toluene,acetone,methanol, alcohol, ester and insoluble in water (10μg/l) . 4. Specification: The product contains not less than 92.0% of 22,23 dihydro-avermectinB1a and the sum of B1a and B1b is not less than 97.0% B1a. 5. Indications: The antibiotic exerts activity against nematode, hookworm, worm insect,worm and acarid hosted in animal gastrointestinal tract. 6. Storage: Kept in a well-closed container and protected from light.