Profit after tax dropped 12 per cent to USD 1.56 billion in the three months to the end of September compared with the third quarter of 2012, GSK said in a statement.
Sales in China slumped 61 per cent, it added.
GSK had previously said that its financial performance in China would take a hit from Beijing's probe into bribery allegedly carried out by senior staff, resulting in little change to its share price in today's trading.
"At this stage, it is still too early for us to quantify the longer-term impact of the investigation on our performance in China," GSK chief executive Andrew Witty said in the earnings statement.