"Between 160 and 190 out of 18,000 members (have defected). This is an insignificant number," Gintautas Paluckas told the Žinių Radijas radio station.
Eleven lawmakers last year left the LSDP political group in the Seimas after the party withdrew from the ruling bloc with the Lithuanian Farmers and Greens Union (LVŽS) to form a new political group in the parliament.
Part of these lawmakers earlier this year founded the LSDDP.
"It was the group in the parliament that split, not the party," Paluckas said.
The opposition LSDP group currently has eight seats in the parliament.