FBR Fibria Celulose S.A.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

Report of Foreign Private Issuer

Pursuant to Rule 13a-16 or 15d-16 of

the Securities Exchange Act of 1934

Dated October 1, 2018

Commission File Number: 1-15018

Fibria Celulose S.A.

Fidêncio Ramos, 302 — 3rd and (part of) 4th floors

Edifício Vila Olímpia, Torre B, Bairro Vila Olímpia

04551-010, São Paulo, SP, Brazil

(Address of principal executive offices)

(Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.)

Form 20-F: x Form 40-F: o

(Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1)):

Yes: o No: x

(Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7)):

Yes: o No: x

(Indicate by check mark whether the registrant by furnishing the information contained in this Form, the Registrant is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.)

Yes: o No: x

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b):

FIBRIA CELULOSE S.A.

Publicly-Held Company

Corporate Taxpayer ID CNPJ/MF no. 60.643.228/0001-21

Company Registry (NIRE) 35.300.022.807 | CVM Code no. 12793

NOTICE TO THE MARKET

FIBRIA CELULOSE S.A. (“ Fibria ” or “ Company ”) (B3: FIBR3 | NYSE: FBR) hereby informs its shareholders and the market in general that on September 28, 2018 the Board of Directors became aware of the resignation presented by Mr. Paulo Fernando Fleury da Silva e Souza as member of the Board of Directors, which became effective on the same date.

Paulo Fernando Fleury da Silva e Souza held the position of member of the Company’s Board of Directors since April 2017.

We extend our deepest gratitude to Mr.  Paulo Fernando Fleury da Silva e Souza for his contribution to the Company’s success over the last years.

São Paulo, October 1, 2018.

Guilherme Perboyre Cavalcanti

Financial and Investor Relations Officer

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