Major attention has been focused on dendrimer-DNA complexes because of their applications in gene delivery systems. Dendrimers are also used to transport miRNA and siRNA in vitro. We examine the interaction of tRNA with several dendrimers of different compositions, mPEG-PAMAM (G3), mPEG-PAMAM (G4), and PAMAM (G4) under physiological conditions using constant tRNA concentration and various dendrimer contents. FTIR, UV-visible, and CD spectroscopic methods as well as atomic force microscopy (AFM) were used to analyze the macromolecule binding mode, the binding constant, and the effects of dendrimer complexation on RNA stability, aggregation, particle formation, and conformation. Structural analysis showed that dendrimer-tRNA complexation occurred via RNA bases and the backbone phosphate group with both hydrophilic and hydrophobic contacts. The overall binding constants of KmpEG-G3 = 7.6 (+/- 0.9) x 10(3) M-1 KmPEG-G4 1.5 (+/- 0.40) x 10(4) M-1, and K-PAMAM-G4 = 5.3 (+/- 0.60) x 10(4) M-1 show stronger polymer-RNA complexation by PAMAM-G4 than pegylated dendrimers. RNA remains in the A-family structure, whereas biopolymer aggregation and particle formation occurred at high polymer concentrations.