In a statement, the airline said net income during the quarter dropped to US$572mln, or 80 US cents a share, from the US$622mln or 84 US cents a share, recorded a year earlier.
Excluding non-recurring items, adjusted earnings per share stood at 96 US cents, which was comfortably above market consensus of 88 US cents.
In the quarter, a one-time charge of US$150mln was recognised due to the tax reform legislation.
Total revenue rose 8% to US$10.25bn, also outstripping market consensus for US$10.13bn, on the back of a 7% hike in total passenger revenue and a 18% jump in other revenues.
Load factor in the quarter also improved to 85.2% from 85.1% previously.
Delta Air said it is now expecting total unit revenue growth in the first quarter to come in between 2.5% to 4.5%.
In premarket trade, Delta Air was up 2.85% at US$57.45.