Extensive photometric monitoring of KH 15D, an enigmatic variable in the young star cluster NGC 2264, has been conducted. Simultaneous and accurate near-infrared photometry (JHK_s bands) between 2003 December and 2005 March is presented, covering most of the variable phase. The infrared variability is characterized by a large-amplitude and long-lasting eclipse, as observed in the optical. The period of variability is 48.3 ± 0.2 days, the maximum photometric amplitude of variability is ～4.2 mag, and the eclipse duration is ～0.5 in phase units. These are consistent with the most recent period, amplitude, and duration in the optical. The blueing of the J—H color (～0.16 mag) during eclipse, which has been suggested before, is unambiguously confirmed; a similar blueing at H—K_s is less clear but is probably present at a similar level. The overall shape of the JHK_s light curves is very similar to the optical one, including a fair time symmetry and less stable flux during eclipse, with a slight hump near zero phase. Most of these variability features of KH 15D observed at near-infrared wavelengths can be explained with the recent model that employs an eclipse by an inclined, precessing disk and an outer scattering region around a pre-main-sequence binary.
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