Welcome to the Esri Forums. It's generally best to try searching on the content of your question before adding a new one. For example, a search on "maximum length" in the lower search box above ("Search Forums" from Geodatabase & ArcSDE) returned eight threads (not including yours) and two of them had the information Nidhin provided.
Reading other posts also provides feedback on how to write a good question. You should make sure to specify which version (and service pack) of ArcGIS software you are using in every query. Here in Geodatabase & ArcSDE, we'll also need to know which database you're using (database product and exact release or service pack).
If you mean something other than field name maximum length, and it's not covered by the comprehensive list of name limits, then please clarify your question.
The character limit(30), which I mentioned yesterday was for ArcSDE on Oracle. I did a quick test and observed that character limit for field name in Arcsde on SQL Server is 31.
