The monthly purchasing managers' index, an important gauge of conditions among companies, rose in the eurozone to 53.1 in September, up from 52.0 in August, according to S&P Global.
Economists had expected an average reading of 51.7. The upturn in economic activity is mainly in the services sector.
An index above 50 is considered to indicate a growing economy.
The trend is similar in the two largest economies, Germany and France, and it is in the services sectors that things are improving, while industry is somewhat weaker. The composite index for industry and services rose sharply compared with August, and more than expected.
