For April-July, the annual output growth was 2.5%, data showed.
The production of crude oil declined by 0.5%, refinery products by 2.7%, fertiliser by 0.3% and cement by 2%, as per official data.
Coal output growth decelerated to 0.7% last month as against 4.1% in July 2016.
According to data, natural gas output rose by 6.6% in July.
Steel production and power generation rose to 9.2% and 5.4%, respectively in July this year from 0% and 2.1% in the same month last year.
Cumulatively, the eight core sectors in April-July recorded a growth of 2.5% as against 6% in the same period a year ago.
Slow growth in key sectors would also have implications on the Index of Industrial Production (IIP) as these segments account for about 41% to the total factory output.