You can use that <Microsoft.VisualBasic.ComClass()> Public Class Class1 declaration.

The same thing can be done from the IDE. Move the cursor to the line Public Class Class1 . Now the Properties window shows Class1 properties and there's the "COM Class" setting. If the properties window is not visible, go to "View\Properties Window" -menu or press F4 in the IDE. I would have added a picture here but that doesn't seem possible.

And you are using VB.NET, right? I noticed your other question about VB6 DLL...