The latest Manufacturing Institute of Supply Manager's Report On Business registered 54.8 percent, climbing above March, when the index was at 53.4 percent.
The index, which shows business expansion when above 50 percent, rose farther than economists had predicted. The forecast was for the index to slide to 53 percent.
In April, the New Orders Index jumped to 58.2 percent from 54.5 percent.
The Employment Index, which has stayed above 50 percent for 31 consecutive months, rose from 56.1 percent to 57.3 percent.
In March, 16 of the 18 manufacturing industries reported growth. Furniture and related products topped the growth list, followed by printing, machinery production, nonmetallic mineral production and miscellaneous manufacturing.