Constantius II or Ivlian

[Marcus Aurelius]

Looks like Constantius II but i guess it is Julian II...Any help would be appreciated.

[agord]

Constantius II, Julian would not have a diadem. All Spes Republice  coins from Sirmium for Julian are as Caesar and bare headed.
Your coin would be RIC VIII Sirmium 81.

[Marcus Aurelius]

Thank you.... i was confused with this Julian coin with diadem,Constantinopolis mint
So,only Julian Spes Republice coins minted in SIRM are without diadem...is that right?

[agord]

The Spes coins minted while he was Caesar are bare headed, those minted after he took the title Augustus diademed. If my quick check is correct only 6 of the mints had issues with Julian as Augustus.
 

[SC]

This type appears (looking at mint mark evidence) to have been struck for Julian as Augustus at some Western mints before Constantius' death - i.e. under Julian's control after he had been proclaimed Augustus in the West in February 360 but before Constantius died in November 361.  He is usually beardless on such coins.

They were also struck for Julian as Augustus after Constantius' death at three eastern mints - Cyzicus, Nicomedia and Alexandria.  He is sometimes portrayed bearded at the first two.

In any event, coins of this type from Sirmium with diademed bust must be Constantius II.

Yours has quite nice reverse details for the type.

SC