Branched and linear polyethylenimines (PEIs) have been studied as efficient and versatile agents for gene delivery in vitro and in vivo. PEIs exist in a linear or branched topology and are available in a wide range of molecular weight (Mw). Most studies have been done using PEIs with Mw higher than 10Kd. This study was aimed to test the transfection efficiency and the cell viability following gene delivery using PEI of Mw 2Kd, a relatively lower Mw cationic polymer. We used murine interleukin-2(mIL-2) plasmid DNA complexed with branched PEI 2Kd or 25Kd, and transfected them into a myoblast muscle cell line, C2C12. The cellular uptake of mIL-2 plasmid DNA was determined using quantitative polymerase chain reaction. RNA transcript levels were studied in the myoblast cells. Our results show that PEI 2Kd was as effective as PEI 25Kd in celluar gene delivery and transfection efficiency in C2C12 cells. Moreover, MTT assay indicated that PEI 2Kd/DNA complexes did not significantly reduce the cell viability regardless of N/P ratios. These results suggest that PEI of Mw 2Kd might play a role as effective and low toxic nonviral vector systems for muscular cell lines.