Method for preparing a modified glycoprotein with the general structure (MLON> = CH) nP- (CH> = NO-L-M ) m (formula I), wherein M and optionally M are independently a polymeric moiety to increasing the molecular weight of the modified glycoprotein, and wherein L and L independently represent a bivalent linking group, and P represents a glycoprotein comprising one or more end terminals oxidized glycan of said glycoprotein, O, N , C and H represent oxygen atoms, nitrogen, carbon and hydrogen respectively, n is 1-10, m is 0-50, the method comprising the steps of: a) oxidizing periodate ions at least one terminal end of glycan present in glycoprotein P *, wherein P * represents a plurality of glycoforms for P- glycoprotein (CHO) n + m containing one or more aldehyde groups, and b) reacting P (CHO) n + m with MLO-NH2 to obtain the modified glycoprotein with the structure (ML-O15 N> = CH) nP- (CHO) m, c) reacting any aldehyde group unreacted in glycoprotein structure (MLON> = CH) nP- (CHO) m with M- L-O-NH2 to obtain the modified glycoprotein with the structure (MLON > = CH) nP- (CH> = NO-L-m ) m wherein said periodate ions are present in an amount of 0.1-5 equivalents relative to the number of terminal ends of nonreducing glycan present in the glycoprotein, and wherein said modified glycoprotein has improved pharmacological properties compared to the glycoprotein starting P * and has retained its functional activity, and wherein P is selected from FVII, FVIII and FIX.Método para preparar una glicoproteína modificada con la estructura general (M-L-O-N>=CH)n-P-(CH>=N-O-L-M)m (fórmula I), en la que M y opcionalmente M son independientemente un resto polimérico para aumentar el peso molecular de la glicoproteína modificada, y en la que L y L representan independientemente un grupo de unión bivalente, y en la que P representa una glicoproteína que comprende uno o más extremos terminales de glucano oxidado de dicha glicoproteína, O, N, C y H representan átomos de oxígeno, nitr
