The so-called "variant words" are two or more words which have exactly the same pronunciation and meaning yet different written forms. They are variants for each other or one another. This study explores categories of variant words in Tang dynasty Kaishu, the standard script. Besides preface and conclusion, there are four chapters specifically exemplifying four categories of variant words in Tang dynasty kaishu, including 1. Variants resulting from corruption, 2. Variants resulting from taboo, 3. Variants resulting from Empress Wu Zetien's coinage, and 4. Variants resulting from different font origin.