The figure was up 15.9 percent year-on-year and up 9.4 percent from last month, according to a report from the Civil Aviation Authority of Vietnam.
The delay fights accounted for 18.2 percent of total flights operated by the country's six carriers last month, it said.
Low-cost carrier Vietjet Air has the industry's highest rate of flight delays at 24 percent, followed by Vietnam Airlines (20.1 percent).
CAAV said late-arriving aircraft was the main cause of delays in addition to other excuses like poor management and bad weather.
The Ministry of Transport said the increase in flight delays has triggered public outcry among passengers and damaged the industry's reputation.
It ordered airlines to ensure flights are punctual, especially during the peak summer travel season.
In the first half of this year, the number of passengers going through Vietnam's airports reached 43.35 million, a pickup of 65.5 percent from a year ago and equivalent to 76 percent of pre-pandemic levels, according to the CAAV.
The CAAV forecast airports nationwide would serve about 87.8 million passengers this year, jumping 190 percent from last year.
The figure includes five million foreign travelers, up 844 percent.