Exhibit 5.1

BeOne Medicines Ltd. (f/k/a BeiGene, Ltd.) / Form S-4 Post-Effective Amendment No. 1

We have acted as special Swiss counsel to BeOne Medicines Ltd., a company limited by shares pursuant to Article 620 et seq. of the Swiss Code of Obligations of March 30, 1911, as amended, incorporated under the laws of Switzerland (the Company), in connection with (a) its change of jurisdiction of incorporation from the Cayman Islands to Switzerland through a transaction known as a continuation (the Continuation) under Section 206 of the Companies Act of the Cayman Islands, as amended, and Article 161 of the Swiss Federal Act on Private International Law of December 18, 1987, as amended, and (b) the filing of the Post-Effective Amendment No. 1 (the Amendment) to the Registration Statement on Form S−4 (Registration No. 333-281324), as amended, (the Registration Statement), which was initially filed with the United States Securities and Exchange Commission (the SEC) under the Securities Act of 1933, as amended (the Act) by BeiGene, Ltd., formerly an exempted company with limited liability incorporated in the Cayman Islands, with registered offices at c/o Mourant Governance Services (Cayman) Limited, 94 Solaris Avenue, Camana Bay, PO Box 1348, Grand Cayman KY1-1108, Cayman Islands (BeiGene Cayman), prior to the effectiveness of the Continuation (the Effective Time). The Company is filing the Amendment to expressly adopt the Registration Statement as its own for all purposes of the Act and the Securities Exchange Act of 1934, as amended, and to reflect the completion of the Continuation.

As such counsel, we have been requested to give our opinion as to certain legal matters under Swiss law.

Capitalized terms used but not defined herein have the meanings assigned to such terms in the Documents (as defined below).

This opinion is confined to and given on the basis of the laws of Switzerland in force at the date hereof. Such laws and the interpretation thereof are subject to change. This opinion is also confined to the matters stated herein and the Documents (as defined below), and is not to be read as extending, by implication or otherwise, to any other document referred to in any of the Documents or any other matter.

For purposes of this opinion, we have not conducted any due diligence or similar investigation as to factual circumstances that are or may be referred to in the Documents, and we express no opinion as to the accuracy of representations and warranties of facts set out in the Documents or the factual background assumed therein.

In this opinion, Swiss legal concepts are expressed in English terms and not in their original language. These concepts may not be identical to the concepts described by the same English terms as they exist under the laws of other jurisdictions.

For purposes of this opinion, we have only reviewed the following documents (collectively, the Documents):

In rendering the opinion below, we have assumed the following:

Based on the foregoing and subject to the qualifications set out below, we are of the opinion that:

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We have issued this opinion as of the date hereof and we assume no obligation to advise you of any changes in fact or in law that are made or brought to our attention hereafter.

We hereby consent to the filing of this opinion as an exhibit to the Amendment. In giving such consent, we neither hereby concede that we are within the category of persons whose consent is required under Section 7 of the Act, or the rules or regulations of the SEC thereunder, nor thereby admit that we are experts with respect to any part of the Registration Statement, as amended by the Amendment, within the meaning of the term “expert” as used in the Act or the rules and regulations promulgated thereunder.

This opinion is governed by and shall be construed in accordance with the laws of Switzerland.

Sincerely yours,

HOMBURGER AG