| Honorific Prefix: | Saint |
| Vasilissa of Nicomedia Василисса Никомидийская | |
| Birth Date: | 300 |
| Death Date: | 309 |
| Feast Day: | 16 September |
| Venerated In: | Eastern Orthodox Church Roman Catholic Church |
| Death Place: | Nicomedia |
| Titles: | Child Martyr |
Vasilissa (300–309) was a Roman Christian girl who is venerated as a child martyr by the Russian Orthodox Church. According to tradition, she was a small child when martyred, suffering in Nicomedia not long after the death of St. Anthimus. The torturers covered her whole body with wounds, but she remained faithful to Jesus Christ.
According to Holy Tradition, she was tortured with fire and wild beasts, yet remained unharmed. Her torturer, Alexander, seeing these wonders, repented and became a Christian. Vasilissa is said to have gone into a field, and fallen to her knees in prayer, thanking God for her endurance under torture, and whilst praying, she was martyred. She died in 309.