According to Šiauliai County police, the incident took place at 7.30 p.m. when a man came from behind, covered the mouth of the soldier, 36, and placed the blade of a utility knife to her throat.
The woman suffered shock.
The attacker, 23, was detained and taken into custody.
Portuguese, Spanish and French troops are now deployed in Šiauliai as part of the NATO air policing mission.