The delegation arrived in Sofia Wednesday after being invited by Bulgaria's Center for Global and Middle East Studies, the Sofia news agency reported.
On Friday, security forces kicked the delegation out of the country.
Hamas spokesman Taher al-Nunu blasted the Bulgarian government for bowing to Israeli pressure.
"We condemn this act, which reflects the scale of compliance with Zionist pressures," Nunu said.
The security agency said although the delegation arrived in Bulgaria legally, "information was received which gives reasons to believe that their presence poses a serious threat for national security."
Ahmed Madbouh, the Palestinian ambassador in Bulgaria told Ma'an news agency the Bulgarian foreign ministry said they "regret" allowing the Hamas delegation into the country and made the decision to ask them to leave.
The delegation's visit to Bulgaria came just a week after Bulgaria accused Hezbollah of carrying out a bus bombing last July that killed Israeli tourists in the Black Sea city of Burgas. Hezbollah denied the accusations.