UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of report (Date of earliest event reported): October 15, 2015

CSX CORPORATION

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (904) 359-3200

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

On October 15, 2015, CSX Corporation (the “Company”) entered into an Underwriting Agreement (the “Underwriting Agreement”) with Citigroup Global Markets Inc., J.P. Morgan Securities LLC and Morgan Stanley & Co. LLC, as representatives of the Underwriters named therein (the “Underwriters”) for the public offering of $600,000,000 aggregate principal amount of the Company’s 3.350% Notes due 2025 (the “Notes”). The Notes were issued pursuant to an indenture, dated as of August 1, 1990, between the Company and The Bank of New York Mellon Trust Company, N.A. (formerly known as The Bank of New York Trust Company, N.A.), successor to JPMorgan Chase Bank, N.A. (formerly known as The Chase Manhattan Bank), as trustee, as supplemented by a First Supplemental Indenture dated as of June 15, 1991, a Second Supplemental Indenture dated as of May 6, 1997, a Third Supplemental Indenture dated as of April 22, 1998, a Fourth Supplemental Indenture dated as of October 30, 2001, a Fifth Supplemental Indenture dated as of October 27, 2003, a Sixth Supplemental Indenture dated as of September 23, 2004, a Seventh Supplemental Indenture dated as of April 25, 2007 and an Eighth Supplemental Indenture dated as of March 24, 2010 (collectively, the “Indenture”), and an Action of Authorized Pricing Officers dated as of October 15, 2015. The Notes have been registered under the Securities Act of 1933, as amended (the “Act”), by a Registration Statement on Form S-3ASR (Registration No. 333-186715) which became effective February 15, 2013. On October 16, 2015, the Company filed with the Securities and Exchange Commission, pursuant to Rule 424(b)(2) under the Act, its Prospectus, dated February 15, 2013, and Prospectus Supplement, dated October 15, 2015, pertaining to the offering and sale of the Notes.

The form of the Notes is filed as Exhibit 4.2 to this Report, and is incorporated by reference in this Report.

See Item 1.01.

The following exhibits are filed as a part of this Report.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.