In a survey conducted by Realmeter, 65.8 percent of those surveyed said they approved of the way Moon managed state affairs, down 0.7 percentage point from a week earlier.
The weekly survey was conducted Monday through Friday on 2,502 adults throughout the country. It has a margin of error of 2 percentage points and a confidence level of 95 percent.
The drop follows rare rapprochement between the two Koreas, highlighted by a two-day trip of Moon's special envoys to Pyongyang from last Monday.
In the meeting with the South Korean envoys, the North Korean leader expressed his willingness to hold talks with the South Korean president and with US President Donald Trump to discuss the possible denuclearization of his country.
Seoul has agreed to hold what would be a third inter-Korean summit in late April, while the US president said he will meet Kim before the end of May.
The local pollster attributed the drop in Moon's approval rating to the recent series of sexual scandals involving Moon's close aides or political allies, including Park Soo-hyun, former spokesman for the presidential office Cheong Wa Dae, and An Hee-jung, former governor of South Chungcheong Province.
"The slight drop appears to have been caused by the sexual assault and sexual harassment allegations involving the former South Chungcheong Province governor and other figures from the ruling bloc, offsetting the diplomatic achievements of Moon's special North Korea envoys, which included a US-North Korea summit," it said in a press release.
The ruling Democratic Party's approval rating dropped 1.9 percentage points to 48.1 percent, with that of the main opposition Liberty Korea Party slipping 0.5 percentage point to 19.2 percent.
The approval rating of the minor opposition Bareunmirae Party came to 8.4 percent, up 1.6 percentage points from a week earlier.
The ratings of the progressive Justice Party and the minor Party for Democracy and Peace came to 5.2 percent and 2.6 percent, respectively.(Yonhap)