To make your DLL available in the context of OSGi you have to use the Bundle-NativeCode section in MANIFEST.MF.
For example if your DLL is called “sapjco3.dll” and is in the main path of you bundle you can use.
Manifest-Version: 1.0 Bundle-ManifestVersion: 2 Bundle-Name: Jco Bundle-SymbolicName: com.sap.conn.jco Bundle-Version: 1.0.0 Bundle-ClassPath: sapjco3.jar Bundle-NativeCode: /sapjco3.dll; osname=win32; processor=x86 Export-Package: com.sap.conn.jco,
Many thanks to Matthias Heinrich for the tip.
Update: You can also maintain several architectures at the same time for example:
Bundle-NativeCode: /sapjco3.dll; osname=win32; osname=win64; processor=x86; processor=x86_64