How would I say....?

[rhumba9]

MA TESOL

or

Master's degree in Teaching English to Speakers of Other Languages

Also, in the US it is common to put your credentials after your name, like MA, or PhD, how about in Japan??

[jkid]

I would guess this is how you would say I have a Masters Degree in TESOL.

TESOLの修士を持っているのです.

or TESOL could be translated as

第二言語としての英語教授

so it would be:

第二言語としての英語教授の修士を持っているのです.

That would translate as "I have a Masters Degree in teaching English as a second language."

Edit: Changed ん to の as ん was incorrect.