The company has reported a profit of Rs 2,071.63 crore in the quarter ended September 30, against Rs 2,492.90 crore in the July-September period of 2013-14.
The state-run firm's total income from operations increased to Rs 16,736.63 crore from Rs 16,448.90 crore in the same period last fiscal.
Fuel cost on year-on-year basis went up to Rs 11,439.33 crore from Rs 10,139.25 crore whereas the company's other income fell to Rs 530.69 crore against Rs 627.19 crore, in the corresponding period.
The decline in profit after tax is mainly on account of changes in Tariff Regulations, 2014, the company said in an official statement.
In July, electricity regulator Central Electricity Regulatory Commission (CERC) rejected NTPC's petition seeking changes in the tariff norms from 2014-19.
NTPC had said that its generation incentives should be linked to the actual power produced instead of the supply. CERC, in its order dated June 30, said the risks associated with the business of electricity generation had been taken care of in the 2014 tariff regulations.
In September, NTPC signed an initial agreement with Andhra Pradesh state government to develop 1,000 MW solar power projects at suitable sites in a phased manner. The projects will be implemented on Build-Own-Operate basis in the state.
For the second quarter of FY15, gross generation was 55.421 Billion Units (BUs) against 54.519 BUs in corresponding quarter of previous year.
During the first six months of the current fiscal (April-September), the company's gross power generation grew to 118.554 BUs from 111.524 BUs for the corresponding period in previous year.