How to open Multiple webpage one after another in python?

I'm unsure as to why you're using range(), simply using len(Cn) is enough, however you should change it to i<len(Cn) so you don't go over the index on the last iteration of the while loop.

Additionally, when you break out in your elif statement, you end the loop. I'm unsure if this is what you're trying to do, if you would rather keep parsing through the list simply remove the elif statement. You also would not need your nn list of no variations.

import webbrowser
Cn=('Acharya Girish Chandra Bose College','AJC Bose College','Ananda Mohan College','Asutosh College','Bangabasi College','Barrackpore Rastraguru Surendranath College','Basanti Devi College')

Cnw={'Acharya Girish Chandra Bose College':'http://www.agcbosecollege.org/','AJC Bose College':'http://www.ajcbosecollege.org/','Ananda Mohan College':'http://anandamohancollege.ac.in/','Asutosh College':'http://www.asutoshcollege.in/','Bangabasi College':'http://bangabasi.org/home.php','Barrackpore Rastraguru Surendranath College':'http://www.brsnc.org/','Basanti Devi College':'http://www.basantidevicollege.edu.in/'}

yy=['Y','Yes','YES','y']
nn=['N','NO','no','No','n']
i=0
while i<len(Cn):
    print 'College Name : ',Cn[i]
    a=raw_input('Do u want to visit the website ? (Y/N) :')
    if a in yy:
        webbrowser.open(Cnw[Cn[i]])
    #elif a in nn:
    #   break
    i=i+1

Which gives me the following output:

College Name :  Acharya Girish Chandra Bose College
Do u want to visit the website ? (Y/N) :n
College Name :  AJC Bose College
Do u want to visit the website ? (Y/N) :n
College Name :  Ananda Mohan College
Do u want to visit the website ? (Y/N) :n
College Name :  Asutosh College
Do u want to visit the website ? (Y/N) :n
College Name :  Bangabasi College
Do u want to visit the website ? (Y/N) :n
College Name :  Barrackpore Rastraguru Surendranath College
Do u want to visit the website ? (Y/N) :n
College Name :  Basanti Devi College
Do u want to visit the website ? (Y/N) :n
>>> ================================ RESTART ================================
>>> 
College Name :  Acharya Girish Chandra Bose College
Do u want to visit the website ? (Y/N) :y
College Name :  AJC Bose College
Do u want to visit the website ? (Y/N) :y
College Name :  Ananda Mohan College
Do u want to visit the website ? (Y/N) :y
College Name :  Asutosh College
Do u want to visit the website ? (Y/N) :y
College Name :  Bangabasi College
Do u want to visit the website ? (Y/N) :y
College Name :  Barrackpore Rastraguru Surendranath College
Do u want to visit the website ? (Y/N) :y
College Name :  Basanti Devi College
Do u want to visit the website ? (Y/N) :y
>>>