Gujinzi (ancient and modern characters) refers to characters in different periods that have different forms and structures but mean the same. Characters used in relatively old times are called Guzi (ancient characters) and characters that came into being later are called Jinzi (modern characters).

Gujinzi falls into two categories. In the first category, Guzi and Jinzi have exactly the same meaning such as  (kuai, both mean block) and (yin, both mean drink). While in the second category, the meaning of Guzi and Jinzi is partly the same, such as (they both have something to with sun ) and (they both have something to do with picture).

In the first category, each Guzi has a corresponding Jinzi, while this is not the case with the second category. Jinzi is the product of differentiation in the evolution of Guzi and it might be evolved from the original meaning of Guzi, from the extended meaning of Guzi or phonetically borrowed from Guzi.

Certain characters with over-loaded meaning made communications difficult, while Gujinzi had been created to differentiate meanings. A close relation can be traced between Gujinzi and regularization of Chinese characters: the regularization will not succeed unless it is carried out with the features of Chinese characters as its significant reference.