The study is a two-part (Part A and Part B) randomized double-blind vehicle-controlled multi-center study in a total of 174 participants with moderate to severe glabellar lines. The objective of this study is to test the safety, efficacy, immunogenicity of YY003, and compare to vehicel control, in improving the appearance of moderate to severe glabellar lines.

Inclusion Criteria:

1. Participants (male or female) must be ≥18 years old, at the time of signing the informed consent.
2. At screening and baseline, participants must have moderate to severe glabellar lines at maximum frown (grade 2 or 3 on the relevant 4-point scale), as assessed by both the investigator and the participant.
3. Male or female (inclusive of all gender identities) participants are eligible to participate if they agree to practice adequate contraceptive methods during the study period and for at least 3 months after the study drug administration. Contraceptive use should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.
4. Participant must provide signed informed consent, including compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol.
5. Participant must have the time and ability to complete the study and comply with instructions, at the discretion of the investigator.

Exclusion Criteria:

1. Known allergy or hypersensitivity to any components of the investigational product or any botulinum toxin serotype.
2. A history or presence of ptosis, significant facial asymmetry, excessive dermatochalasis at screening or baseline.
3. A history or presence of facial nerve palsy at screening or baseline.
4. A positive HIV, hepatitis B or hepatitis C test at screening.
5. History or presence of other concomitant diseases which are assessed by the investigator to be unsuitable for participation in this clinical research.
6. History of drug or alcohol abuse.
7. History or presence of epilepsy.
8. Have a serious mental disorder that, in the Investigator's opinion, may affect participant compliance with the study.
9. Female who is pregnant or breast feeding.
10. Abnormal laboratory tests that, in the Investigator's assessment, are not appropriate for participation in this study.
11. Participation in an investigational device or drug study within 30 days or 5 half-lives (whichever is longer) prior to screening.
12. Study center personnel, close relatives of the study center personnel, employees or close relatives of employees at the sponsor company.