Complexes between mRNA and GL67:DOPE:DMPE-PEG5000 (GL67) liposomes were formulated and characterized. Subsequently, the in vitro and in vivo expression characteristics of mRNA/GL67 complexes and pDNA/GL67 complexes, each produced at their optimal ratio, were compared in respiratory cells. Transfection of A549 cells with mRNA/GL67 complexes resulted in a much faster expression than after transfection with pDNA/GL67 complexes. The percentage of GFP-positive cells after mRNA and pDNA transfection peaked after 8 and 24 h, respectively. At these time points the percentage of GFP-positive cells was two times higher after mRNA transfection than after pDNA transfection. Furthermore, the efficacy of mRNA/GL67 complexes was independent of the cell cycle. This was in sharp contrast with pDNA/GL67 complexes that caused only a weak expression in nondividing cells. This confirms that the nuclear barrier is a crucial obstacle for pDNA but not for mRNA. Finally, mRNA/GL67 and pDNA/GL67 complexes encoding luciferase were administered intranasally to the lungs of mice. The mRNA/GL67 complexes did not give rise to a measurable luciferase expression in the murine lungs. In contrast, a detectable bioluminescent signal was present in the lungs of mice that received the pDNA/GL67 complexes. We showed that mRNA/GL67 complexes have a lower stability in biological fluids. Consequently, this may be an explanation for their lower performance in vivo.