I followed the suggestion from this thread as:
{\footnotesize
\bibliography{bibfile}}
The font size is smaller now, but there is a problem as showing below
How can I fix the problem (by adding some space between the header title and the first reference?)
Thanks a lot
Solution
I found this thread
\enlargethispage{10pt}
\bibliographystyle{abbrv}
{\footnotesize
\bibliography{sigproc}}

\vspace{-1cm}– Jérôme Dequeker Oct 04 '16 at 09:24\bibliographystyle{abbrv}and before my command in the first post but nothing changed. – mommomonthewind Oct 04 '16 at 09:28\footnotesizeis after the\begin{thebibliography}command that is generated as part of the.bblfile from bibtex. that, in turn, means that a patch to the environment definition in the document class is probably needed. but first, look into the document class code, and see if there's a definition for\bibliofontor similar; all the ams classes contain such a definition to make such changes possible and reliable. – barbara beeton Oct 04 '16 at 13:24