Production output declined 0.5% from the previous month, following a 0.2% increase in April and flat growth in March, according to the Office for National Statistics, or ONS, Anadolu Agency reported.
The market had expected a monthly decline of 0.1%.
Mining and quarrying output contracted 4.6% in May, while water supply and sewerage production fell 2.4% and electricity and gas output edged down 0.1%.
Manufacturing output rose 0.1%, partially offsetting declines in the other main sectors.
Within mining and quarrying, crude petroleum and natural gas extraction dropped 4.8%, leaving the industry's output at its lowest level since monthly records began in 1990.
Seven of the 13 manufacturing subsectors posted growth in May, led by a 5.3% increase in machinery and equipment production.
That was largely offset by a 2.7% decline in basic metals and metal products.
Over the three months to May, total production output rose 0.1% compared with the previous three-month period, extending growth to a sixth consecutive period.
Manufacturing was the only main sector to make a positive contribution, with output increasing 1.6%.
Electricity and gas output fell 4.3%, its steepest three-month decline since June 2025, while water supply and sewerage dropped 1.9% and mining and quarrying declined 1.5%.
Eight of the 13 manufacturing subsectors expanded over the three-month period, led by a 5.4% increase in basic pharmaceutical products.
Basic metals and metal products rose 2.7%, while food, beverages and tobacco production increased 1.7%.