 <p>I think you shouldn't be touching to the gradle/index.[android¦ios].js files when you change the root directory ; the paths are relatives meaning as long as you don't change your folder hierarchy it will keep working.</p> <p>The best way to add react-native to an existing projet is to first add it via <code>npm</code> :<br> <code>npm install --save react react-native</code></p> <p>Then, copy your <code>android</code>, <code>ios</code> folders and your <code>js</code> files to the root of your project.<br> Copying/merging <code>.flowconfig</code> and <code>.gitignore</code> files is recommended (if you use git and/or flow).</p> <p>You should be able then to start your project using react-native run-android.</p> <p>I think your problem there is that you didn't install the npm packages in the new project (or maybe I am totally wrong)</p>