  Effects of a new triple-{\alpha} reaction rate on the s-process during the
evolution of a massive star of 25 M\odot are investigated for the first time.
Although the s-process in massive stars has been believed to be established
with only minor change, we find that the s-process with use of the new rate
during the core He-burning is very inefficient compared to the case with the
previous triple-{\alpha} rate. However, the difference of the overproduction is
found to be largely compensated by the subsequent C-burning. Since the
s-process in massive stars has been attributed so far to the neutron
irradiation during core He-burning, our finding reveals the importance of
C-burning for the s-process during the evolution of massive stars.
