This trial is conducted in China. The purpose is to evaluate the efficacy, Pharmacokinetics (PK) profile, immunogenicity and safety of GB001 recombinant peptide spray in adults with mild recurrent aphthous ulcer.

Inclusion Criteria:

1. It meets the diagnostic criteria for mild recurrent Aphthous ulcer in the fifth edition of Oral Mucosa published by People's Medical Publishing House in 2020.
2. 18≤ age ≤65 years old, gender is not limited.
3. Patients with untreated target ulcer onset ≤48 hours at the time of screening.
4. VAS score of target ulcer irritation pain ≥3 points, 2mm≤ length diameter of target ulcer ≤10mm.
5. Subjects and their sexual partners agree to use effective contraception during the study period and for at least 30 days after the study ends.
6. Sign a written informed consent, and be able to comply with the visit and related procedures stipulated in the program.

Exclusion criteria:

1. The diagnosis was severe aphthous ulcer, herpetic aphthous ulcer, acute herpetic gingivitis stomatitis, traumatic ulcer, cancerous ulcer, tuberculous ulcer, syphilitic ulcer, necrotic salivate metaplasia, Behcet disease and other diseases or drug induced ulcers.
2. Patients with suppurative tonsillitis or other painful lesions in the mouth, such as pericoronitis, pulpitis, periapical inflammation, etc., affecting the pain score of target ulcer.
3. Target ulcer is affected by residual root, residual crown, denture, prosthesis, orthodontic device and other stimulating factors in the corresponding parts of the target ulcer.
4. The ulcer is located in the lingual frenulum, the back wall of the pharynx and other parts, and its size is not easy to measure.
5. Those who plan to perform other oral treatments during the trial that affect the determination of drug effectiveness and safety.
6. Smokers > 20 cigarettes/day or betel nut lovers in the past 3 months.
7. People who have used painkillers or drugs that may affect the efficacy of pain observation within 24 hours before the first administration, such as sedatives, anti-allergy drugs, non-steroidal anti-inflammatory drugs, etc.
8. Patients who have used antibiotics or antiviral drugs locally or systematically within 1 week before screening.
9. Patients who had used immunosuppressive agents locally within 1 week before screening or systemic immunosuppressive agents within 2 weeks before screening.
10. Patients with oral local or systemic use of glucocorticosteroids within 4 weeks prior to screening.
11. Patients who have taken anticholinergic drugs to reduce salivary secretion within 2 weeks prior to screening.
12. Complicated with severe liver and kidney diseases, or abnormal liver and kidney function tests (ALT and AST≥ 1.5 times the upper limit of normal, SCr > the upper limit of normal).
13. Patients with severe anemia (Hb < 60g/L).
14. Complicated with severe heart and lung disease, uncontrolled diabetes (fasting blood glucose > 7.0mmol/L or random blood glucose ≥11.1mmol/L), advanced tumors, diseases of the blood and hematopoietic system, or other serious or progressive diseases of the system.
15. Known or suspected allergic history or serious adverse reactions to the experimental drug and its excipients.
16. Pregnant or lactating women and those with recent pregnancy plans.
17. Participants who had participated in other interventional clinical trials within 3 months prior to screening.
18. Other conditions deemed inappropriate by the investigator for participation in the study.