Lopaičiai dolmen is a prehistoric megalithic monument located in Lithuania, near the village of Lopaičiai in the eastern part of the country. It is believed to date back to the Neolithic period, around 4,000-2,000 BCE.

The dolmen consists of two upright stones supporting a massive capstone, which forms a chamber or tomb. The capstone is estimated to weigh around 20 tons, making it one of the largest in Lithuania.

The dolmen was discovered in 1958 and excavated in 1961-62 by archaeologist Jonas Balčius. Inside the chamber, Balčius found traces of human bones, pottery fragments, and stone tools, indicating that the monument was used as a burial site.