Make sure your mod_deflate is enable. Check file httpd.conf :
nano /etc/httpd/httpd.conf
Find this :
LoadModule deflate_module modules/mod_deflate.so
Create /etc/httpd/conf.d/deflate.conf with the following contents
nano /etc/httpd/httpd.conf
Find this :
LoadModule deflate_module modules/mod_deflate.so
Create /etc/httpd/conf.d/deflate.conf with the following contents
# Insert filter
SetOutputFilter DEFLATE
# Netscape 4.x has some problems...
BrowserMatch ^Mozilla/4 gzip-only-text/html
# Netscape 4.06-4.08 have some more problems
BrowserMatch ^Mozilla/4.0[678] no-gzip
# MSIE masquerades as Netscape, but it is fine
BrowserMatch bMSIE !no-gzip !gzip-only-text/html
# Don't compress images
SetEnvIfNoCase Request_URI .(?:gif|jpe?g|png)$ no-gzip dont-vary
# Don't compress already compressed stuff !
SetEnvIfNoCase Request_URI .(?:exe|t?gz|zip|bz2|sit|rar)$ no-gzip dont-vary
SetEnvIfNoCase Request_URI .pdf$ no-gzip dont-vary
# Make sure proxies don't deliver the wrong content
Header append Vary User-Agent env=!dont-vary
# Log Stuff !
#DeflateFilterNote Input input_info
#DeflateFilterNote Output output_info
#DeflateFilterNote Ratio ratio_info
#LogFormat '"%r" %{output_info}n/%{input_info}n (%{ratio_info}n%%)' deflate
# CustomLog /var/log/httpd/deflate_log deflate
Now, you have enable your compression