Markit Economics and HSBC Bank released its index the emerging markets on Thursday. The Emerging Markets Index fell to 50.7 in May from 51.3 in March. It was the lowest level since May 2014.
A reading above 50 indicates an expansion of the activity.
The fall was driven by a decline in services and manufacturing sectors.
"Growth of emerging markets ground almost to a halt in May, according to the latest PMI surveys, highlighting the deepening malaise facing many parts of the global economy," Markit's Chief Economist Chris Williamson noted.