EXHIBIT 5.1

[Letterhead of Christopher O’Brien, Esq.]

November 12, 2002

Mattel, Inc.

333 Continental Boulevard

El Segundo, California 90245-5012

Re:    Registration Statement on Form S-8

Ladies and Gentlemen:

I am the Vice President, Assistant General Counsel and Assistant Secretary of Mattel, Inc., a Delaware corporation (the “Company”). I am delivering this opinion in connection with the registration under the Securities Act of 1933, as amended (the “1933 Act”), of 6,600,000 shares of common stock, par value $1.00 per share (the “Shares”) of the Company, which are to be offered and sold by the Company pursuant to the Amended and Restated Mattel 1996 Stock Option Plan, as amended (the “Plan”).

This opinion is delivered in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the 1933 Act in connection with the Registration Statement on Form S-8 that relates to the proposed issuance and sale of the Shares pursuant to the Plan (the “Registration Statement”). Such Registration Statement is being filed with the Securities and Exchange Commission (the “Commission”) under the 1933 Act.

In rendering the opinion set forth herein, I have made such investigations of fact and law, and examined such documents and instruments, or copies thereof established to my satisfaction to be true and correct copies thereof, as I have deemed necessary under the circumstances. In some instances, I have relied upon other attorneys in the Company’s Law Department.

Based on and subject to the foregoing and subject further to the assumptions set forth below, I am of the opinion that the Shares, when offered, sold and paid for pursuant to the terms and conditions of the Plan, will be duly authorized and validly issued, fully paid and non-assessable.

I express no opinion other than on the laws of the State of California and the General Corporation Law of the State of Delaware (the “DGCL”) insofar as the DGCL relates to corporate formalities, including statutory and reported decisional law thereunder, and I express no opinion with respect to the applicability thereto, or the effect thereon, of the laws of any other jurisdiction or, in the case of Delaware, any other laws, or as to any matters of municipal law or the laws of any local agencies within any state.

I hereby consent to the filing of this opinion as an exhibit to the Registration Statement. In giving such consent, I do not thereby admit that I am in the category of persons whose consent is required under Section 7 of the 1933 Act or the rules and regulations of the Commission thereunder.

Very truly yours,

/s/    CHRISTOPHER O’BRIEN        

Christopher O’Brien, Esq.

Vice President, Assistant General Counsel

and Assistant Secretary