In a speech at a secondary school, he said he would never forget the images of “misery and ruin”.
It comes a day after his successor, Barack Obama, said New Orleans was “moving on” from the disaster.
Hurricane Katrina killed nearly 2,000 people and displaced one million.
It was the most expensive natural disaster in US history, causing destruction along the Gulf coast from Florida to Texas. But the city of New Orleans, in Louisiana, bore the brunt.
George Bush’s administration’s slow response to the disaster remains a source of deep resentment in the city.
Mr Bush began speaking at 10:30 local time (15:30 GMT) at Warren Easton Charter High School on Friday.
His wife, Laura, who also spoke, helped raise money to save the school.
On Thursday, President Obama spoke from the Lower Ninth Ward, a mostly African-American neighbourhood still recovering from the disastrous 2005 storm.
“This community centre stands as a symbol of the extraordinary resilience of this city and its people, of the entire Gulf Coast, indeed, of the United States of America,” he told residents.
It was the president’s ninth trip to the city since the hurricane struck. When he was a presidential candidate in 2008, he criticised his predecessor’s administration for its poor handling of the crisis.
“What started out as a natural disaster became a man-made disaster, a failure of government to look out for its own citizens,” he said on Thursday.
The storm broke the levees that were supposed to keep New Orleans from flooding.
But Mr Obama said on Thursday the city had since become a model for the rest of the nation “in disaster response and resilience”, stressing the importance of other cities investing in storm preparation for disasters caused by global warming..
Despite massive destruction, the city has risen anew out of the storm.
New Orleans’ rebirth has been bolstered by billions of federal dollars, largely spurred by Mr Obama.
The city has recovered much of its population lost during the storm as new businesses emerge and tourists visit the city, famous for its jazz music, unique food and party culture.
Despite those strides, income inequality and crime still plague the city, which Mayor Mitch Landrieu calls “America’s Comeback City.”
When Hurricane Katrina struck, the staff of a New Orleans radio station fought to keep listeners alive through the deadly winds, rain and floods.