>My C# Winforms application uses same datareader query a lot of times and it is allowed that it can use cached result from previous datareader creation.
>
>How to cache result obtained by datareader in memory so that in next time
>cached query result is returned instead of makng trip to server?
>
>Or is it better to use DataTable and cache DataTable in memory?

In the example you describe it is better to use a DataTable and then only refresh the DataTable whenever needed (i.e. make a trip to the server)