Those users who are new to the world of VPS hosting commonly ask if they are able to run an unlimited number of websites and while a number of companies will answer yes, the truth is you are limited to the amount of resources you have assigned to your virtual private server.

The first limitation is going to be the control panel you have installed and the number of domains it can host.   For example, cPanel comes in a couple variations including those that can handle up to 10 or up to 100 websites.  If you have a control panel with limited domain name allowed, there’s your first limitation.
The second limitation to the number of websites you can host is the amount of hard drive space you have allotted to your VPS account.  Each website that you create requires a footprint and storage space to host all of the information and store all of your data.  Depending on the size of your website and the scripts you use, this can take up as little as a meg to hundreds of megs of disk space.

Lastly you will not want to overload your VPS account to the point that the CPU and RAM cannot quickly process all the information your visitors require.  While your new sites may not require a huge deal of resources due to the smaller amounts of initial traffic you will be receiving, as they continue to grow they are going to require more resources to serve the information to your visitors.  By hosting too many websites on the same virtual private server, you could exhaust its resources and slow down loading times or even crash the VPS account.

If a VPS hosting provider tells you that you can host unlimited numbers of websites without informing you of the above limitations, you may want to consider another company for your web hosting needs, as they are not being entirely truthful.