The event was organised by the Manila city government along with the United Nations Children's Fund (Unicef) and local health officials. The aim was to increase public awareness about the benefits of breast-feeding, and turn mothers away from using baby formula.
Dale Rutstein, the Unicef Philippines spokesman, said: "We are confident that we broke the record."
Elvira Esguerra, a doctor and one of the organisers, said a total of 3,738 mothers took part in the mass breast-feeding.
According to the World Health Organisation, about 16,000 children die every year in the Philippines because their milk formula is mixed with dirty water or the wrong amount of powder.
Only 16% of Filipino mothers breast-feed their children for the first six months of their lives, local health authorities say.
The previous record for the largest number of women simultaneously breast-feeding was 1,135 in the Californian city of Berkeley in 2002.