Bremen-based AN has 1,300 wind power systems with a combined capacity of around 1,300 megawatts and employs some 200 people, Siemens said in a statement.
AN’s capacity represents around 8 percent of the total in Germany, the world’s biggest wind market by installed capacity.
The company is a close partner of Bonus Energy, the Danish wind-energy firm Siemens bought last year.
"With the acquisition of this company we want to further expand our market share in Germany," Siemens Power Generation unit head Andreas Nauen said in the statement.
The global wind power market is seen growing by around 17 percent annually on average in the coming years as governments increasingly rely on an expansion of wind energy to curb greenhouse gas emissions, which are blamed for global warning.
Siemens said it already had approval from German anti- trust authorities and could close the deal by the end of the year.