Brazil being the largest in South America by land area, Suriname is the smallest.

Republic of Suriname is a country on the northeastern Atlantic coast of South America. It is bordered by the Atlantic Ocean to the north, French Guiana to the east, Guyana to the west, and Brazil to the south. At 163,820 square kilometers (64,000 square miles), it is the smallest sovereign state in South America.

It has a population of approximately 575,990 with population density of 2.9 / km2

The land area of the 4 mentioned answers are:

Suriname - 163,820 km2 (63,251 sq mi)

Uruguay - 176,215 km2 (68,037 sq mi)

Guyana - 214,969 km2 (83,000 sq mi)

Ecuador - 283,561 km2 (109,484 sq mi)

More Info: en.wikipedia.org