Speaking on Sunday as he prepared to leave for New York, Ahmadinejad said that the 40-year-old treaty had failed in its objective of preventing the spread of nuclear weapons.
"The IAEA (International Atomic Energy Agency) in the past 40 years has not been successful in its mission," he said.
"We have no disarmament or non-proliferation and some countries have even procured the nuclear bomb during this period."
Amadinejad is expected to defend Iran's right as a signatory to the NPT to enrich uranium for civilian purposes, a programme which Western powers say is masking a covert drive to acquire nuclear weapons.
Tehran has refused to abandon its enrichment programme and now faces the prospect of UN-backed sanctions as a result of its defiance in the face of international pressure.
Ahmadinejad denies Iran is seeking to develop nuclear weapons and says the NPT needs to be reformed.
"This is an important meeting," he said. "For some time now, committees have been formed to undertake a fundamental revision (of the NPT) in order to achieve the aims for which the IAEA was formed."
Hillary Clinton, the US secretary of state, will address the conference hours after Ahmadinejad. She cautioned last week that any efforts to disrupt the talks will fail.
"If President Ahmadinejad wants to come and announce that Iran will abide by their non-proliferation requirements under the NPT, that would be very good news indeed," she said on Thursday
Clinton she said if he tried to "divert attention from this very important global effort or cause confusion that might possibly throw into doubt what Iran has been up to ... I don't believe he will have a particularly receptive audience".
The month-long NPT review conference is held twice a decade to discuss the implementation of the treaty, which calls on signatories to abandon nuclear weapons and to prevent the spread of the technology.
Ban Ki-moon, the UN secretary-general, said over the weekend that more progress needs to be made in disarmament efforts, which have been boosted by new pledges from the US and Russia in recent months.
Ban also said Iran's and North Korea's nuclear programmes were "of serious
concern to global efforts to curb nuclear proliferation".