The purpose of this study is to evaluate the Efficacy and Safety of MT921 in Subjects with Moderate to Severe Submental fat compared with Placebo.

Inclusion Criteria:

1. Adults 19~65 years of age
2. CA-SMFRS and PA-SMFRS score of 2 or 3
3. Satisfaction level is 3points or less
4. Voluntarily provide informed consent

Exclusion Criteria:

1. Following history that can affect the efficacy and safety evaluation in the chin or neck area as judged by the investigator

   • Scars or skin lesion on the study treatment region
   • Liposuction or lipolytic material treatment to decrease submental fat
   • Permanent filler, synthetic implantation and autologous fat grafting
   • Within 1 year of screening visit, semi-permanent filler (Calcium Hydroxyapatite, collagen-stimulator, etc.), radio-frequency treatment, HIFU, thread, laser procedure and chemical peeling procedure over medium-depth
   • Within 6 months of screening visit, temporary filler (Hyaluronic acid, etc.) procedure on the chin or neck, injection of botulinum toxin, radio-frequency treatment, HIFU, thread, laser procedure and chemical peeling procedure over medium-depth

2. BMI over 35.0 kg/m^2

3. Submandibular enlargement due to causes other than localized subcutaneous fat (hyperthyroidism, cervical lymphadenopathy, etc.)

4. Current or past dysphagia

5. Judged difficult to measure submandibular fat due to sagging skin on the chin and neck or wide platysmal bands on the neck

6. Bleeding or taking anticoagulant drugs (except for patients taking anticoagulant drugs, those who can discontinue administration from 3 days before injection to 24 hours after injection of the IP)

7. Skin disease or would infection on the study treatment region

8. Hypersensitivity to Lidocaine, Benzocaine, Procaine or the IP

9. Pregnancy or breast feeding or female of child-bearing potential who has not agreed to use of medically acceptable contraception during the study period

   • All women of childbearing age have negative pregnancy test results can be enrolled in parallel with surgical sterilization (hysterectomy, bilateral tubal ligation or bilateral oophorectomy) or menopause (amenorrhea for more than 12 months).
   • Medically acceptable contraception: Intrauterine device, Intrauterine system, vasectomy, tubal ligation, condom, Cervical cap, Contraceptive diaphragm, contraceptive sponges, spermicide, oral contraceptive pill and etc.

10. Experience of other clinical trials within 30 days before screening

11. Any other clinically meaningful conditions that are considered ineligible for the study in the medical judgement of principal investigator or sub-investigator