jQuery could do that on the client side very simply.
However, if you want to do it in code behind:
<ItemTemplate >
<asp:CheckBox ID="CheckBox1" runat="server" AutoPostBack="True"
oncheckedchanged="RepeaterCheckBox_CheckedChanged"/>
protected void RepeaterCheckBox_CheckedChanged(object sender, EventArgs e)
{
foreach (RepeaterItem RE in Repeater1.Controls)
{
foreach (Control C in RE.Controls)
{
CheckBox CB = C as CheckBox;
if ((CB != null) && (CB != sender))
CB.Checked = false;
}
}
}