There are different settings when exporting video. It sounds like you're on an uncopressed one, and that is sometimes the best choice. If for example you are going to take that into Premiere or After Effects, and the video has an alpha channel, your final composition will be the best quality.
If instead you're making an animation to go straight to YouTube, or some other sharing site, there is an option in the export for H.264. Choose that one, and you will get an MP4 that is more like 60 MB.