How do I justify frequent job changes in an interview? I am planning to change 3rd company within a year.

This is one way to justify your change for the third time within a year. 'Unfortunately both the previous 2 jobs have not challenged me enough.

I dont know what line of profession you are engaged in. I dont know what exactly are the reasons for change of job. Whether it is wise to change so frequently depends on the context, but generally around 2 years in a job is the norm. Rolling stones gather no moss.

But this is one way to justify your change for the third time within a year. 'Unfortunately both the previous 2 jobs have not challenged me enough. The promised challenges have not materialised. It is for this reason that I am looking at this job change'.