 <p>Is it of correct architecture? Did you define <code>ABI</code> for the .so file? Is it marked as <code>AndroidNativeLibrary</code>?</p> <pre><code>&lt;ItemGroup&gt; &lt;AndroidNativeLibrary Include="path/to/libfoo.so"&gt; &lt;Abi&gt;armeabi&lt;/Abi&gt; &lt;/AndroidNativeLibrary&gt; &lt;/ItemGroup&gt; </code></pre> <p>Just in case here is the documentation: <a href="http://developer.xamarin.com/guides/android/advanced_topics/using_native_libraries/" rel="nofollow">http://developer.xamarin.com/guides/android/advanced_topics/using_native_libraries/</a> <a href="http://www.mono-project.com/docs/advanced/pinvoke/" rel="nofollow">http://www.mono-project.com/docs/advanced/pinvoke/</a> Pretty sure you've seen it though.</p>