The results mirror similar patterns which are emerging with its rival Apple, which also saw a slump reduction on its iPhone sales and a predicted fall in China sales.
Samsung reported a four-percent fall in second-quarter profit and ruled out a "special dividend" similar to a big year-end pay-out for 2014.
Samsung's dominance is being chipped away at the low-to-mid end by Chinese rivals such as Huawei Technologies, while China follows some markets show signs of saturation.
Samsung is still the top smartphone maker in April-June, but shipments fell in part due to an inability to build enough curved-screen Galaxy S6 edge handsets.
The firm said its mobile division will launch new larger-screen phones in the third quarter but may not improve earnings.
Second-quarter profit was $5.9 billion, matching the company's estimate issued earlier this month.
"While 2H 2015 is expected to present mounting challenges, the company will try to improve earnings," Samsung said.
Samsung's mobile business booked a 38 percent decline. It expects smartphone shipments to rise in the third quarter from the second, but said average selling prices could fall due to price adjustments for S6 models aimed at boosting sales.
The firm has brought forward the launch of its latest Galaxy Note phone to August from September. Rumours are that it plans a larger version of the S6 edge.
Samsung's chips division reported profit of $290 million, its highest since the third quarter of 2010, due to demand for memory chips and sales growth in mobile processors.