I am using a kendo library for my project. I have to load 250 rows in a kendo grid but rendering is very slow & after loading the page becomes unresponsive. When i checked in the firebug i found kendo.all.min.js file size is(2.37 MB) which is cached by browser. does it impact on rendering
This has nothing to do with kendo.all.min.js being cached or not, it's just to do with your data set. Think about it, kendo is having to manipulate the DOM for 250 rows and it will get worse as the data set grows. You can test this yourself by reducing the number of rows to, for example, 20 and you will see that the browser renders it quicker.
Generally, if you're using Kendo with ASP.NET, your Kendo helper inside the view is actually rendering a script on to the page. When that page loads fully, the kendo.all.min.js file will then convert this into a Grid. Of course, ignore this if you're doing this all server side.
Finally, although this has no bearing on the question, don't use kendo.all.min.js unless you're using each component inside this file. You'll just need kendo.grid.js and it's dependencies. In web terms 2.37mb is huge for a .js file. Each person who visits your website has to download a file that size and it will impact on their load times hugely.