Eni's net profit for the third quarter declined by 57.8% to $1.83bn (€1.24bn) from $4.34bn (€2.94bn) in the same period last year.
The decline was attributed to lower operating performance from the exploration and production division, which was affected by weaker oil and gas prices, the company said in a statement.
Other influential factors included lower operating results from the downstream oil business due to unprofitable refining margins.
Operating profit for the quarter was $4.73bn (€3.21bn), a 48.4% drop compared with $9.2bn (€6.24bn) in Q3 2008.
The company's oil and natural gas production for Q3 2009 was 1.68 million barrels per day, representing a 4.9% drop compared with 1.76 million barrels per day in Q3 2008.
Eni's net profit for the first nine months of 2009 was $5.86bn (€3.97bn), representing a 59% drop compared with $14.3bn (€9.69bn) for the same period in 2008.
Oil and natural gas production for the first nine months of 2009 was 1.73 million barrels per day, a decline of 2.6% compared with 1.77 million barrels per day for the same period last year.
Operating profit for the initial nine months of 2009 was $14.15bn (€9.59bn), representing a 47.3% decrease compared with $26.86bn (€18.2bn) for the same period last year.
The decreases were primarily attributed to Opec production cuts, security concerns in Nigeria, weaker production uplifts related to low European gas demand and mature field declines, the company said.