He said the "smooth transition" of such a huge measure in a vast country involving crores of people was historic and can be a case study for universities around the world.
The prime minister said the priority of the government, while ushering in the GST (Goods and Services Tax), has been that there should no burden on the plate of the poor man.
In his monthly radio programme 'Mann Ki Baat', Modi also spoke about various other issues like the flood situation in various parts of the country and mentioned about the freedom movement in view of the upcoming Independence Day.
In the 30-minute broadcast also stressed the need for using only the environment-friendly items made by the poor people of the country during the festivals and hailed the performance by the Indian Women's Cricket team in the recent World Cup.
Referring to the GST which was rolled out on July 1, the prime minister said, "one nation, one tax -- how big a dream has been fulfilled."
Underlining that GST is more than just a tax reform, he said it ushers in a new culture.
"It has been about a month since the GST was implemented and I feel satisfied and happy when someone writes to me to say how the prices of goods needed by the poor have reduced," Modi said.
"GST has transformed the economy," Modi said.
"GST, which I call 'Good and Simple Tax', has really made a very positive impact on our economy and in such a short span of time," he added.
He said the speed at which the smooth transition, migration and new registration has taken place has led to a new confidence in the country.
Describing GST rollout is an example of cooperative federalism, the prime minister said all states are partners in it and have a responsibility as well. "All decisions were taken by the Centre and the states through consensus," he said.
Modi said is an example of success of the collective effort of India and marks a "historic achievement".
He said it was not only a tax reform but "is a measure that lends strength to the new culture of honesty. In a way it is campaign for cultural improvement."
The prime minister said the magnitude of the exercise is an example in itself and will surely be studied by the world.
Modi said the people from the North East, far off mountains and those living in the jungles have written letters, saying that initially there were fears but as they started understanding the GST, it became easy and business became easier.
"And the biggest thing is that the trust of customers in traders has started going up," the prime minister said.
"I am seeing how GST has impacted upon the transport and logistics sector, how the movement of trucks has increased, how their travel time has decreased, how highways have become clutter-free.
"With the increase in the speed of trucks, pollution has also reduced. Delivery of goods has also been speeded up. Besides making life easier, it also strengthens the economic progress," he said.
PTI