The Swift/UVOT began observerving the field of GRB 100728B 101s after the BAT trigger (Morris et al., GCN 11009). We detect the optical afterglow in the white, v, b and u filters only. The refined UVOT position is RA (J2000)= 163.48809, DEC (J2000)=-45.47265, which is equivalent to: RA (J2000) = 02:56:13.467 Dec (J2000) = +00:16:52.18 with an estimated uncertainty of 0.52 arcsec (radius, 90% confidence). This position is consistent with the XRT refined position (Evans et al., GCN 11017) and with the optical afterglow positions reported by KAIT (Perley et al., GCN 11007, 11010 & 11024), PROMPT (Ivarsen et al., GCN 11008, 11011) & the SON-NM observatory (Elenin et al., GCN 11012). The non-detection in the UV filters suggests a photometric redshift of z~2.8. Preliminary magnitudes and the 3 sigma upper limits are reported below for individual optical images and summed UV images. Filter T_start(s) T_stop(s) Exposure Mag/3SigUL ########################################################### white 101 251 147 17.43 +/- 0.08 white 4713 4913 197 20.62 +/- 0.22 v 3687 3887 197 20.19 +/- 0.56 b 4509 4709 197 20.47 +/- 0.33 u 4303 4503 197 19.90 +/- 0.28 uvw1 4098 6050 294 > 20.50 uvm2 3892 5529 393 > 20.52 uvw2 3482 5119 393 > 20.93 ########################################################### The above magnitudes are not corrected for the Galactic extinction corresponding to a non-negligible reddening of E_{B-V} = 0.07 mag (Schlegel et al., 1998, ApJS, 500, 525). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383,627).