We present the second Swift Ultra-Violet/ Optical Telescope (UVOT) gamma-ray burst (GRB) afterglow catalog, greatly expanding on the first Swift UVOT GRB afterglow catalog. The second catalog is constructed from a database containing over 120,000 independent UVOT observations of 538 GRBs first detected by Swift, the High Energy Transient Explorer. 2 (HETE2), the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), the Interplanetary Network (IPN), Fermi, and Astro-rivelatore Gamma a Immagini Leggero (AGILE). The catalog covers GRBs discovered from 2005 January 17 to 2010 December 25. Using photometric information in three UV bands, three optical bands, and a "white" or open filter, the data are optimally coadded to maximize the number of detections and normalized to one band to provide a detailed light curve. The catalog provides positional, temporal, and photometric information for each burst, as well as Swift Burst Alert Telescope and X-ray Telescope (XRT) GRB parameters. Temporal slopes are provided for each UVOT filter. The temporal slope per filter of almost half the GRBs are fit with a single power. law, but one to three breaks are required in the remaining bursts. Morphological comparisons with the X-ray reveal that similar to 75% of the UVOT light curves are similar to one of the four morphologies identified by Evans et al. (2009). The remaining similar to 25% have a newly identified morphology. For many bursts, redshift-and extinction-corrected UV/ optical spectral slopes are also provided at 2 x 10(3), 2 x 10(4), and 2 x 10(5) s.