after rendering video has a transparency.

problem solved trikmat i choose alpha instead of matte

That is a media player. Media players do not support transparency. To check for transparency you need to open the file in After Effects or Premiere Pro.

* The "Drag & Drop here..." area is buggy and should not be used to share images. Please use the toolbar or just drag your images to the reply field.

Without any info about actual render settings and what the layers look like in the comp and timeline nobody can tell you much. From effects producing a different look at different bit depths to issues with hardware accelerated processing messing up things this could be anything. You have to be more specific.

Mylenium