To identify the ethnicity of a last name, first examine the suffix of the last name, as you can usually determine the ethnicity from it. For example, typical French suffixes include "-eau," "-el," "-iau," "-on," "-ot". Russian last names usually end in "-ev," "-in," "-ov," "-sky." For a female last name, add "a" in the end of a suffix.
Prefixes can also help to determine the ethnicity. For example, some Arabic prefixes include "Al-", "El-". Prefix "De-" indicates that the last name is Belgian.
If you are still not sure about the origin of the last name, try to find it in a book, such as "The Story of Our Names" by Elsdon C. Smith's or "The Dictionary of American Family Names". These books have lists of many last names, including some rare ones, together with explanations about their ethnicity.
Ancestor Search, Ancestry.com and Genealogy.com are genealogy websites that have databases of last names. To find information about a last name, type it into one of the websites' search engines, and click search. However, users usually have to pay to use these websites.
If you want to save some money, try to find the last name on Wikipedia, as it has information about some of the most common last names. There is usually information about which region of the world the last name came from and what meaning it may have.