Old Sugar Mill of Koloa, Sugar mill ruins in Koloa, Hawaii.

The Old Sugar Mill of Koloa is a historic industrial ruin in the town of Koloa, on the island of Kauai, Hawaii, listed as a National Historic Landmark. What remains today is a stone chimney and foundation walls from the 19th century, with on-site information panels explaining how the facility once operated.

Ladd & Company founded Hawaii's first commercially successful sugarcane plantation here in 1835, leasing 980 acres from King Kamehameha III but planting only 12 that September. A water-powered mill produced molasses in 1836, and by 1837 output reached over 4,000 pounds of sugar. A second mill with the surviving stone chimney was built on Waihohonu Stream from 1839 to 1841 for close to US$16,000. Ladd & Co. shut down in 1844; the plantation passed to Robert Wood, and in 1853 a steam engine powered a mill in Hawaii for the first time.

Workers from China, Japan, the Philippines, and Portugal came to work at the mill and brought their languages, foods, and festivals with them. Traces of that community are still visible on Kauai today, in local cooking, family names, and annual celebrations.

The site sits in the center of Koloa town and is easy to reach on foot or by car. The ground around the ruins is uneven in places, so sturdy shoes are a good idea before you walk around.

The first mill of 1836 ran on water from the Maulili pool, but in 1853 a steam engine powered a mill in Hawaii for the first time, here at Koloa. The stone chimney and foundations visible today belong to the larger mill built on Waihohonu Stream between 1839 and 1841, which cost close to US$16,000.