  We have performed the near-infrared photometric monitoring observations of
two TeV gamma-ray binaries with O-stars (LS 5039 and 1FGL J1018.6-5856), using
IRSF/SIRIUS at SAAO, in order to study the stellar parameters and their
perturbations caused by the binary interactions. The whole orbital phase was
observed multiple times and no significant variabilities including orbital
modulations are detected for both targets. Assuming that the two systems are
colliding wind binaries, we estimate the amplitude of flux variation caused by
the difference in the optical depth of O-star wind at inferior conjunction,
where the star is seen through the cavity created by pulsar wind, and other
orbital phases without pulsar-wind intervention. The derived amplitude is
<0.001 mag, which is about two orders of magnitude smaller than the observed
upper limit. Also using the upper limits of the near-infrared variability, we
for the first time obtain the upper limit of the dust formation rate resulting
from wind-wind collision in O-star gamma-ray binaries.
