Lastheneia (or Lasthenia) of Mantinea (Greek: Λασθένεια Μαντινική) was one of Plato's female students.
She was born in Mantinea, an ancient city in Arcadia, in the Peloponnese. She studied in the Academy of Plato dressed as a man. After the death of Plato she continued her studies with Speusippus, Plato's nephew. She is also said to have had a relationship with Speusippus.
A papyrus fragment from Oxyrhynchus mentions an unidentified woman who studied under Plato, Speusippus, and then Menedemus of Eretria. The fragment goes on to explain that "in her teens she was lovely and full of unstudied grace." This woman is probably Lastheneia or Axiothea of Phlius.