A device for reconstituting an active ingredient in the form of sterile powder, comprising: - a vial containing said active ingredient as sterile powder having a mouth and a pierceable closing member which closes the mouth ; - a flexible bag containing a sterile liquid; - a connecting component fixed to the vial and to the flexible bag ; - an axially perforated spike , constrained to the connecting component and adapted to pierce the closing member , said spike comprising a tip , facing towards the closing member , and a head opposite to the tip , wherein the axially perforated spike is inserted in a hole of the connecting component , and wherein there is provided a pierceable membrane which seals said hole , characterized in that the device further comprises - a sealing member which seals the closing member at the mouth , having an open central portion and arranged so as to leave a central portion of the closing member uncovered; - an elastomeric sealing ring arranged between the connecting component and the closing member of the vial ; in that the connecting component comprises an annular seat where the elastomeric sealing ring is partially accommodated, in that the elastomeric sealing ring is in contact with the sealing member ; in that there is provided a hermetically sealed sterile chamber , delimited by the closing member , by the connecting component and by the elastomeric sealing ring , the hermetically sealed sterile chamber being an empty space delimited at the top by the piercable sealing membrane and by the connecting component , laterally by the elastomeric sealing ring , and at the bottom by a part of the upper side of the sealing member and by the uncovered central portion of the closing member ; in that the connecting component is provided with a plurality of coupling teeth which fix the connecting component to the vial , the coupling teeth being in abutment against the portion of sealing member that covers a step of the vial so that the elastomeric sealing ring is subjected to compression, so as to ensure the tightness of the hermetically sealed sterile chamber ; in that the axially perforated spike is adapted to slide from a rest position inside the flexible bag to a working position, piercing the piercable sealing membrane before crossing the hermetically sealed sterile chamber and piercing the closing member when a pressure is exerted on the head with at least one finger of a hand, allowing the passage of the sterile liquid from the flexible bag to the vial , and of the reconstituted active ingredient from the vial to the flexible bag , whereby the active ingredient is reconstituted in sterile conditions. - a vial containing said active ingredient as sterile powder having a mouth and a pierceable closing member which closes the mouth ; - a flexible bag containing a sterile liquid; - a connecting component fixed to the vial and to the flexible bag ; - an axially perforated spike , constrained to the connecting component and adapted to pierce the closing member , said spike comprising a tip , facing towards the closing member , and a head opposite to the tip , - a sealing member which seals the closing member at the mouth , having an open central portion and arranged so as to leave a central portion of the closing member uncovered; - an elastomeric sealing ring arranged between the connecting component and the closing member of the vial ; <EOS>