Try to below code:
Dim oda As OleDbDataAdapter = New OleDbDataAdapter
con = New OleDbConnection("..........")
con.Open()
oda.SelectCommand = New OleDbCommand
oda.SelectCommand.Connection = con
oda.SelectCommand.CommandText = "select * from Tablename"
Try
dr = oda.SelectCommand.ExecuteReader
Catch ex As Exception
MessageBox.Show(ex.ToString)
End Try
ComboBox1.Items.Clear()
While dr.Read
ComboBox1.Items.Add(dr.Item(0))
End While
dr.Close()