The surplus was recorded with imports falling sharper than exports, the Central Bureau of Statistics (BPS) said.
Imports shrank 7.16 percent to US$11.51 billion in September from US$12.4 billion in August and exports fell 1.55 percent to US$12.5 billion from US$12.7 billion in the same period.
BPS chief Suryamin said the country has always recorded trade surplus this year on sharper fall in imports.
Suryamin said surplus in trade of commodities other than oil and gas was recorded at US$1.48 billion, up from US$330 million in August.
The surplus in September brought the countrys total surplus to US$7.13 billion in the first nine months of the year as against a deficit of US$1.67 billion in the same period last year.