3C 66A is one of the most interesting blazars and one of our monitoring objects carried out with the 1.56 m telescope at Sheshan station, Shanghai Astronomical Observatory (ShAO). It has been monitored since 1996 December 11. In the present work, we show its optical light curves during the period of 1996 December 11-2009 December 28. From our observations, we found that the largest variations in the V, R, and I bands are {Delta}V=1.840+/-0.065, {Delta}R=1.898+/-0.069 mag, and {Delta}I=1.659+/-0.047 mag, respectively. Intra-day variabilities are found in the three bands: in the V band, an A=17.7% brightness increase over {Delta}T=47.5 minutes on JD 2455119, and an A=46.27% brightness increase over {Delta}T=271.4 minutes on JD 2454816; in the R band, an A=47.09% brightness increase over {Delta}T=23.18 minutes on JD 2454004, and an A=38.11% brightness increase over {Delta}T=87.98 minutes on JD 2453995; and in the I band, an A=13.2% brightness decrease over {Delta}T=38.44 minutes on JD 2453995, and an A=92.8% brightness decrease over {Delta}T=344.02 minutes on JD 2454818. For micro-variability, we found that R variability leads I variability by 25.92+/-1.09 minutes. When the periodicity analysis methods, with the red noise being considered, are adopted to the V, R, and I observations, we can find that the periodogram to the V data is consistent with red noise, except for 1 CLEANest peak corresponding to the timescale of 696.0+/-182.0 days, those to the R data are 653.0+/-171.0 and 156.0+/-17.0 days; and those to the I data are 801.0+/-207.0 and 156.0+/-15.0 days, respectively.