The environment secretary said organic food was more of a "lifestyle choice that people can make".
There is no "conclusive evidence either way" concerning the health effects of pesticides, he told the Sunday Times.
The Soil Association, which regulates organic food, said studies show a difference between organic food and food produced using industrial methods.
It was critical of Mr Miliband's suggestion that food grown with the use of pesticides and other chemicals should not be regarded as inferior.
Mr Miliband: "It's only 4% of total farm produce, not 40%, and I would not want to say that 96% of our farm produce is inferior because it's not organic."
He said despite the rise in organic sales being "exciting" for shoppers, they should not think of conventionally-produced food as "second best".
Source: BBC News