FrameParent.aspx

<form id="form1" runat="server">
<asp:Label id="Label1" runat="server" Text="FrameParent.aspx Label1.Text"></asp:Label>
<iframe id="IFrame1" src="TestFrame1.aspx" frameborder="1" scrolling="AUTO" title="TestFrame1" />
<iframe id="IFrame2" src="TestFrame2.aspx" frameborder="1" scrolling="AUTO" title="TestFrame2" />
</form>

TestFrame1.aspx

<form id="form1" runat="server">
<div>
<asp:Label id="Label1" runat="server" Text="TestFrame1.aspx Label1.Text"></asp:Label>
<input type="button" onclick="onShowParentButtonClick();" value="Show Parent" />
<input type="button" onclick="onShowFrame2ButtonClick();" value="Show Frame2" />
</div>
</form>

<script type="text/javascript">
<!--
function onShowParentButtonClick()
{
alert(window.parent.document.getElementById('Label1').innerHTML);
}
// -->
</script>

<script type="text/javascript">
<!--
function onShowFrame2ButtonClick()
{
alert(top.frames['IFrame2'].document.getElementById('Label1').innerHTML);
}
// -->
</script>

TestFrame2.aspx

<form id="form1" runat="server">
<div>
<asp:Label id="Label1" runat="server" Text="TestFrame2.aspx Label1.Text"></asp:Label>
</div>
</form>

How to use i frame in asp.net with dynamic height

Try This : public partial class Form1 : Form { public Form1() { InitializeComponent(); List<KeyValuePair<int, string>> data = new List<KeyValuePair<int, string>>(); KeyValuePair<int, string> item; for (int i = 1; i < 10; i++) { item = new KeyValuePair<int, string>(i, "Item " + i.ToString()); data.Add(item); } listBox1.DataSource = data; listBox1.DisplayMember = "Value"; listBox1.ValueMember = "Key"; } private void button1_Click(object sender, EventArgs e) { KeyValuePair<int, string> item = new KeyValuePair<int,string>(11,"Item 11"); List<KeyValuePair<int, string>> data = (List<KeyValuePair<int, string>>)listBox1.DataSource; data.Add(item); listBox1.DataSource = null; listBox1.DataSource = data; } }