Developed by Denef-Loeser more than one decade ago, motivic Milnor fiber was a power tool to study singularities from the point of view of motivic integration. Especially, the impressive appearance of Kontsevich-Soibelman's theory of motivic Donaldson-Thomas invariants around 2008 two of whose foundations are the conjectural integral identity and the motivic Thom-Sebastiani theorem once again proves the importance of motivic Milnor fiber in different fields of mathematics. Recently, after works of Hrushovski-Loeser, one can describe motivic Milnor fiber in a more model-theoretical way. I used this new description to prove the integral identity conjecture for algebraically closed fields. More recently, during my visit at the ICTP in October 2013, using the same method, I was able to recover the motivic Thom-Sebastiani theorem. We shall introduce how to prove these results in the talk. Some comments on open problems concerning motivic Milnor fiber will be also given.