The present invention relates to a method for treating or preventing fibrosis and improving kidney function comprising administering a Hovenia dulcis Thunb extract and/or a Lindera obtusiloba extract to the subject. The method of the present invention can lower the level of GOT, GPT, ALP, BUN and total bilirubin; improve kidney functions; lower the amount of hydroxyproline in liver but increase the amount of hydroxyproline in kidney, suggesting that the extract above has excellent anti-fibrosis and kidney protecting effects; lower the level of malondialdehyde, suggesting that the extract has excellent anti-oxidative effect; and promote cell viability in liver and kidney cell lines, indicating that the extract has excellent liver and kidney cell protective effects.