Presence of abundant pores and highly entangled nanotubes make bucky paper (BP) a natural candidate for filtration related applications. Both single- and multiwall carbon nanotube (SWNT and MWNT) BPs were fabricated via self-assembly. Average diameter of the pores on the surface of MWNT BP appeared to be 33 ± 15 nm. However, due to the high tortuousity of BP, the cutoff size, estimated by filtration of colloidal dispersions of Au and CdS nanoparticles of different diameters, turned out to be 4−5 nm. The particle sizes were verified using microscopic and spectroscopic methods. The flux of Au nanoparticle solutions through BP was about 1000 L h⁻¹ m⁻² bar⁻¹. Highly flexible and robust SWNT BPs were prepared very easily, even without proper dispersion. It was found that the crystallinity and purity of the SWNTs had a bigger role than the quality of dispersion in determining the final mechanical strength of BP. The density of SWNT BP was estimated to be 1.3 ± 0.3 g/cm³ after correcting for the weights of the impurities. This is among the highest ever reported. The average wall to wall separation of adjacent tubes was estimated to be 0.35 ± 0.2 nm, which is very close to the ideal value. The SWNT BP was also found to be impervious to liquids such as water, n-hexane, acetone, and isopropyl alcohol, indirectly verifying its close knit structure and small pore size. This is indicative of its possible use as a molecular sieve membrane.