HANOI, June 26 (Reuters) - Vietnam's State Treasury raised 13.55 trillion dong ($532 million) in an auction where it had offered 15 trillion dong of government bonds at the Hanoi Stock Exchange on Wednesday, with coupons falling for the first time this year.

The amount is higher than the $323 million raised last week, a bourse filing showed. The uptake was also higher, with 90% of the offer sold, up from 78% in last week's auction.

The Southeast Asian country is aiming to raise 400 trillion dong from government bond sales this year mainly to fund its public investments, one of the key drivers of economic growth.

The State Treasury sold all of the 12 trillion dong of 10-year bonds offered on Wednesday with a coupon of 2.74%. It sold all of the 1.5 trillion dong of 15-year bonds offered with a coupon of 2.86%. The coupons were 2.76% and 2.88% in its previous auction, respectively.

It sold only 50 billion dong out of 500 billion dong of 30-year bonds offered with a coupon of 3.1% and failed to offload any of the 1 trillion dong of 5-year bonds offered.

Vietnam has so far this year raised 155 trillion dong from government bond sales, according to data from the exchange.

Companies in Vietnam raised 107 trillion dong from corporate bond issuances in the year to June 21, according to data from the Vietnam Bond Market Association. (Reporting by Khanh Vu Editing by Ed Davies)