The effect of the alkyl side group on the synthesis and the electrochemical properties of N-alkyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR1ATFSI) ionic liquids (ILs) is reported. The investigation was focused on the PYR1ATFSI ionic liquid family because of the interesting electrochemical properties of the members with propyl and butyl side chains. Side alkyl groups (A=C n H2n+1 with n ranging from 1 to 10) of different length and structure were used for the synthesis of PYR1ATFSI materials. NMR and DSC have shown that the ionic liquids were correctly synthesized with the exception of the compounds with tertiary side chains. Most of the materials exhibited a conductivity higher than 10−3 Scm−1 already at 12°C. In the molten state a moderate conductivity decrease was observed with increasing the length and the branching of the side chain (C2H2n+1) group according with the change of viscosity of the ionic liquids. Most of the PYR1ATFSI samples exhibited an electrochemical stability window exceeding 5V.