 <p>The code sample you provided will not work. You need to return the new size or pass in the reference to the form object.</p> <pre><code> public void SetFormProperties(Form form){ fprm.Size = new Size(20,20); } SetFormPropertoes(form); </code></pre> <p>OR</p> <pre><code> public Size GetFormSize(){ return new Size(20,20); } from.Size = GetFormSize(); </code></pre>