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 March 31, 2017

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 ”) (BM&FBOVESPA: FIBR3 | NYSE: FBR), in order to update the information released to the market in the Material Fact of May 14, 2015 and the Notice to the Market of August 29, 2016, hereby informs its shareholders and the market in general that it has already concluded eighty-seven percent (87%) of the physical execution related to the expansion plan of the Company, which consists in the construction of a the second line of pulp production in Três Lagoas, in the State of Mato Grosso do Sul, referred to as Horizonte 2 Project with a nominal pulp capacity of 1.95 million tons.

With that, the Company anticipated the planned startup of the new pulp production line, that initially was for the beginning of the fourth quarter of 2017, bringing it to the beginning of September 2017 (third quarter).

The Horizonte 2 Project will expand Três Lagoas unit’s annual pulp production capacity to 3.25 million tons. In 2017, the new pulp production line is expected to produce a volume of 377 thousand tons.

Fibria underlines, accordingly, by means of the release of the information in this Notice to the Market, its commitment to transparency with its shareholders and investors.

São Paulo, April 3, 2017.

FIBRIA CELULOSE S.A.

Guilherme Perboyre Cavalcanti

Chief Financial and Investor Relations Officer

1