| Full Name | Lee Young-seo |
| Stage Name | Youngseo |
| Native Name | 이영서 |
| Birthday | November 13, 2005 |
| Age | 19 years and 7 months old |
| Zodiac Sign | Scorpio |
| Birthplace | Seoul, South Korea |
| Height | 5’6″ (168 cm) |
| Weight | – |
| Blood Type | A |
| MBTI | ESTJ |
| Education | Gaepo High School |
| Languages | Korean, English |
| Group | ALLDAY PROJECT |
| Social Media | Instagram: [@youngseo] |