This was due to a slowdown in agriculture, construction and transport sectors, data showed on Thursday.
The government sees Tanzania's economy growing by 7.4 per cent this year from an estimated 7.2 per cent in 2014 due to expected strong performance of agriculture, construction and manufacturing sectors.
Growth in agriculture, the biggest contributor to the economy, slowed to 2.4 per cent from 4.5 percent previously, said the state-run National Bureau of Statistics (NBS) in a report.
Construction expanded by 15 per cent in the third quarter of 2014 versus a 16.3 per cent expansion previously, while transport also slowed to 13.9 per cent from 19.3 per cent previously.
Manufacturing bucked the trend, expanding 10.8 per cent in the third quarter of 2014 versus 10.4 percent previously.
Other sectors that improved include information and communication, which rose by 11.9 per cent compared with 7 per cent previously, while the mining and quarrying sector rose by 5.2 per cent from 3.3 per cent previously.
“Diamond production in the third quarter of 2014 rose to 66,508 carats from 27,828 carats produced during the same period in 2013,” said NBS, pointing to the expansion in mining.
Tanzania is Africa's fourth largest gold producer, but also produces diamond, tanzanite and other precious stones.
Gold production fell to 10.137 tonnes in the third quarter of last year from 11.01 tonnes previously, the data showed.
Tanzania's gross domestic product expanded by 32 per cent in 2013 to 69.8 trillion Tanzanian shillings after the state rebased its calculation to incorporate new sectors in the economy, including big discoveries of natural gas.