"From the German point of view, it's possible to change the treaty if it makes sense," Merkel said at a joint press conference. "If we can say why, what for, what the point is, then Germany will be ready."
Macron has proposed a eurozone budget, finance minister and parliament and in Berlin declared that Europe has reached a "historic moment", faced with "the rise of populisms" and the danger of disintegration of the EU.
Before his visit officials had said it was "not realistic" to propose amending EU treaties, a process that requires the agreement of all member countries.
But Merkel has said that it is vital for Macron to succeed with many German politicians frightened of the prospect of the Eurosceptic National Front winning the French presidency in five years' time.
German public opinion
While promising to make big changes in France, Macron even challenged Merkel to confront German reluctance to pay more in the interest of European reform.
"I believe in mutual confidence," he said. "To achieve that, each side has to do what is necessary. I have to make thoroughgoing reforms that are necessary for our country. Madame Chancellor has a job to do convincing public opinion."
But he tried to answer German concern about shouldering the debts run up by other eurozone countries, saying he opposed the "mutualisation of old debts", while adding that joint financing of future projects should be considered.