Belfast's MAC is the 500th member of Breastfeeding Welcome Here, in which venues show their support for the scheme by displaying a pink sticker.
A list of scheme members - from cafÃ©s to libraries and church halls - can be found on the BreastFedBabies website.
The Department of Health says NI's breastfeeding rates have remained static for several years.
Mothers in Northern Ireland who choose to breastfeed also do so for a shorter period than breastfeeding mothers elsewhere in the UK, according to department figures.
The Breastfeeding Welcome Here initiative is being led by the Public Health Agency (PHA) and is designed to show community support for breastfeeding mothers.
Janet Calvert of the PHA said World Breastfeeding Week from 1-7 August offered an important opportunity to get that message across.
"Breastfeeding is the best start in life," she said.
"Showing increased support for breastfeeding mums is really important, as Northern Ireland has the lowest breastfeeding rates in the UK and one of the lowest rates in Europe.
"We know that for many mums, getting started isn't easy.
Information and support is essential, both before baby is born, and especially in the early days, so that mums can build their confidence and stay with their decision to breastfeed.
In January, the then health minister Michelle O'Neill promised to bring forward legislation as soon as possible to protect mothers who breastfeed in public.
This was shortly before the collapse of Northern Ireland's power-sharing executive.
Venues across Northern Ireland are being encouraged to sign up to a major breastfeeding support scheme.