The growth in e-book sales comes as the company reported a rise in digital sales through its website and a decline in sales through its physical bookstores during the fourth quarter. In February, B&N said it was selling two times more e-books than physical books. Physical books still generate more sales volume, however.

B&N sells e-books through its Nook e-reader and through its Nook application for third-party devices such as smartphones and tablets. The company is adding millions of Nook users each quarter, said CEO William Lynch during an earnings conference call.

The company's overall Nook business across devices, accessories and digital content through the physical stores and website grew to over US$250 million, increasing 300 percent compared to the fourth quarter last year, Lynch said. The Nook sales number includes e-book content sold through BN.com. Store sales were $943 million for the quarter, declining by 2.9 percent.

The increasing e-book business did not save the company from a loss, however. For the fourth quarter, the company reported a consolidated net loss of $59 million on total sales of $1.37 billion, compared to a loss of $33 million on sales of $1.32 billion a year earlier.

The company is continuing to invest in the burgeoning digital business, Lynch said. The company expects e-book prices to fall as self-publishing applications gain a foothold, Lynch said. B&N offers Pub!It, which allows independent publishers and authors to upload and distribute works through BN.com and the Barnes & Noble eBookstore.