Is there some tool available through which I can check Alexa ranking in one go? It takes up lot of time to check the URLs one by one and I am required to check lots of URL's alexa ranking.
Yes it would be a tedious task to check a website ranking on Alexa one by one if you had multiple websites. Unfortunately that's the only way to go. I have never encountered a single software which serves you to check multiple domains in one action.
I have never heard of anything that gives alexa ranking for bulk websites. I remember doing the same job for my company and I had to manually put in the alexa for each website.
I tried to find a website that would do this and apparently this one works fine: checkprinbulk.com, just enter all the URLs you want and be patient as it takes a few seconds. I tested it out and it gave me what appeared to be the correct Alexa rank for each site. It'll give you the PR as well which might be useful.
Why do you need the Alexa rankings? They're really fairly useless as they don't really mean anything. PR is not a huge factor anymore but it means more than the Alexa rating.