ADO : ActiveX Data Objects and ADO.Net are two different ways to access database in Microsoft.

ADO

ADO.Net
ADO is base on COM : Component Object Modelling based. ADO.Net is based on CLR : Common Language Runtime based.
ADO stores data in binary format. ADO.Net stores data in XML format i.e. parsing of data.
ADO can’t be integrated with XML because ADO have limited access of XML. ADO.Net can be integrated with XML as having robust support of XML.
 In ADO, data is provided by RecordSet. In ADO.Net data is provided by DataSet or DataAdapter.
ADO is connection oriented means it requires continuous active connection. ADO.Net is disconnected, does not need continuous connection.
ADO gives rows as single table view, it scans sequentially the rows using MoveNext method. ADO.Net gives rows as collections so you can access any record and also can go through a table via loop.
In ADO, You can create only Client side cursor. In ADO.Net, You can create both Client & Server side cursor.
Using a single connection instance, ADO can not handle multiple transactions. Using a single connection instance, ADO.Net can handle multiple transactions.