Alexander Auldjo (21 October 1758 – 21 May 1821) was a businessman and political figure in Lower Canada.

He became involved in the fur trade and, later, in the export of wheat and the importing of goods from England.

In 1796, he was elected to the Legislative Assembly of Lower Canada for Montreal West.

He was also named a justice of the peace for Montreal district in 1796 and became a warden of Trinity House of Quebec in 1800.

His nephew, George Auldjo, later became a Montreal merchant and a partner in the company formed by his uncle.