Single wall carbon nanotube films (bucky paper) have been prepared using aqueous dispersions containing 0, 3, 6, and 10 M nitric acid. With increasing nitric acid concentration, film tensile strength increased from 10 to 74 MPa, tensile modulus from 0.8 to 5.0 GPa, while in-plane dc electrical conductivity decreased from 3 x 10(4) S/m to 1.2 x 10(4) S/m. In-plane storage modulus exhibited no decrease in the measured temperature range (room temperature to 200 degreesC). Raman spectroscopy showed that nitric acid treatment results in the loss of the small diameter tubes. This was consistent with the X-ray diffraction observation, which showed that with increasing nitric acid concentration, (10) and (11) SWNT d spacings increased from 1.23 to 1.29 nm and from 0.74 to 0.87 nm, respectively. Morphological changes in the film have been monitored using scanning electron microscopy.