X0306 4 2015-09-08 0001177648 ENANTA PHARMACEUTICALS INC ENTA 0001185034 MELLETT PAUL J C/O ENANTA PHARMACEUTICALS, INC. 500 ARSENAL STREET WATERTOWN MA 02472 0 1 0 0 Treasurer and CFO Common Stock 2015-09-08 4 S 0 6792 39.501 D 68605 D Common Stock 2015-09-08 4 S 0 708 40.0597 D 67897 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person in May 2015 to provide liquidity for tax payments due on account of prior option exercises. The price reported in Column 4 is a weighted-average price. These shares were sold in multiple transactions at prices ranging from $38.9700 to $39.9200, inclusive. The price reported in Column 4 is a weighted-average price. These shares were sold in multiple transactions at prices ranging from $39.9750 to $40.3500, inclusive. The reporting person undertakes to provide to Enanta Pharmaceuticals, Inc., any security holder of Enanta Pharmaceuticals, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnotes 2 and 3 above. /s/ Paul J. Mellett 2015-09-10