Many peptide ligands of nicotinic acetylcholine receptors (nAChRs) contain a large number of positively charged amino acid residues, a striking example being conotoxins RgIA and GeXIVA from the marine mollusks venoms, with an arginine content of more than 30%. To check wheth er peptides built exclusively from arginine residues will interact with different nAChR subtypes or with such their structural homologues as the acetylcholine binding protein and ligand binding domain of nAChR α9 subunit, we synthesized a series of R3, R6, R8 and R16 oligoarginines and investigate their activity by competition with radioiodinated α- bungarotoxin, by two electrode voltage clamp electrophysiology and calcium imaging. R6 and longer peptides inhibited muscle type-, α7- and α3β2 nAChRs in the μM range. The most efficient inhibition of ion currents was detected for muscle nAChR by R16 (IC50 157 nM) and for α9α10 subtype by R8 and R16 (IC50 44 and 120 nM, respectively). Since the R8 affinity for other tested nAChRs was 100-fold lower, it appears to be a selective antagonist of α9α10 nAChR. For R8 the electrophysiological and competition experiments indicate the existence of two distinct binding sites on α9α10 nAChR. Since modified oligoarginines and other cationic molecules are widely used as cell penetrating peptides, we studied several cationic polymers and demonstrated their nAChR inhibitory activity. SIGNIFICANCE STATEMENT: By radioligand analysis, electrophysiology and calcium imaging we found that oligoarginine peptides are a new group of inhibitors for the muscle and some neuronal nicotinic acetylcholine receptors (nAChRs), the most active being those with 16 and 8 Arg residues. Such compounds and other cationic polymers are cell penetrating tools for drug delivery and for several of the latter we also demonstrated the inhibition of nAChRs. Possible positive and negative consequences of such an action should be taken into account.