how to insert multiple items of listbox in access database in c#

your

ad.InsertCommand.ExecuteNonQuery();

needs to be inside the for loop.

right now, it is outside the for loop and hence called only one. also because it is a multi row insert you're trying, you're better off wrapping it in a oledb transaction to avoid data loss/inconistencies..

basically,

1. create an OleDbTransaction
2. insert all your records. (by calling ExecuteNonQuery)
3. Commit the OleDbTransaction

It only inserts one row -the last one- because that's how many times you are calling ExecuteNonQuery. If you want to insert every singe row, then move your closing curly bracket right after con.Close();

for (int i = 0; i < listBox1.SelectedItems.Count; i++)
{

   ad.InsertCommand = new OleDbCommand("insert into Map_Data (Material_Code,Product_Id) values(@Material_Code,@Product_Id)", con);

   ad.InsertCommand.Parameters.Add("@Material_Code", OleDbType.Integer).Value =Convert.ToInt32(listBox1.SelectedValue);
   listBox1.Items.Remove(listBox1.SelectedItem);
   ad.InsertCommand.Parameters.Add("@Product_Id", OleDbType.Integer).Value = count;


   con.Open();
   ad.InsertCommand.ExecuteNonQuery();
   con.Close();
}
MessageBox.Show("Record is successfully Save In The Database");

You may want to add some sort of try/catch blocks in case you get problems opening the connection or executing the actual statement itself. Also, you don't need to open/close the connection inside the for loop. It should be enough with opening the connection outside the for and then closing it after the for block. But again, I suggest you add try/catch or use using statements instead.