Hi,
First make sure your are binding list box in this way.
DataTable dtName = new DataTable();
dtName.Columns.Add(new DataColumn("DisplayMember"));
dtName.Columns.Add(new DataColumn("ValueMember"));
dtName.Rows.Add("Suits", "0");
dtName.Rows.Add("Harvey Spector", "1");
dtName.Rows.Add("Jessica Pearson", "2");
dtName.Rows.Add("Mike Ross", "3");
dtName.Rows.Add("Donna Paulson", "4");
dtName.Rows.Add("Rachel", "5");
Listbox1.DataSource = dtName;
Listbox1.DataTextField = "DisplayMember";
Listbox1.DataValueField = "ValueMember";
Listbox1.DataBind();
and on page load you are not rebinding the listbox control i.e place databinding code in if(!ispostback) block.
and simply call
ListItem item = Listbox1.SelectedItem;
string selectedText = item.Text;
string selectedValue = item.Value;
Hope this helps!.