This paper describes the synthesis and structure of protein nanotube (NT) with a lectin interior surface and its size-dependent dextran loading ability in aqueous medium. The NTs were prepared using an alternating layer-by-layer build-up assembly of poly-l-arginine (PLA) and human serum albumin (HSA) in a track-etched polycarbonate (PC) membrane (pore diameter, 400nm), subsequently coating concanavalin A (ConA) as the last layer. Dissolution of the PC template yielded (PLA/HSA)(2)PLA/ConA NTs with 419 +/- 14nm outer diameter and 50 +/- 7nm wall thickness. In a 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) buffered solution, the NTs captured fluorescein isothiocyanate (FITC)-labeled dextran [molecular weight 4kDa, FITC-Dex(4k)] efficiently into the pores. The ratio of the bound FITC-Dex(4kDa)/ConA was estimated to be 2.1 (mol/mol). Two of four glucosyl-residue binding sites of ConA on the wall presumably faced to the aqueous inner phase of the tube, and they can bind FITC-Dex(4k). On the one hand, only half amount of FITC-Dex was loaded into the channels when the molecular weight of the dextran is greater than 20kDa. Small-angle X-ray scattering measurements revealed that the radius of gyration (R-g) of the FITC-Dex(4k) is 1.45nm (5.0mg/ml), which is satisfactorily small to interact with the each binding site of ConA independently. In contrast, the R-g values of FITC-Dex(20k) and FITC-Dex(40k) were 3.75nm (5.0mg/ml) and 6.62nm (4.0mg/ml), respectively. These large dextrans probably formed an equivalent complex with ConA on the tube wall. Copyright (c) 2014 John Wiley & Sons, Ltd.