  This paper investigates the impact of dust size distribution on magnetic
resistivity. In particular, we focus on its impact when the maximum dust size
significantly increases from sub-micron. The first half of the paper describes
our calculation method for magnetic resistivity based on the model of
\citet{1987ApJ...320..803D} and shows that the method reproduces the results of
a more realistic chemical reaction network calculations reasonably well. Then,
we describe the results of the resistivity calculations for dust distributions
with large maximum dust grains. Our results show that resistivity tends to
decrease with dust growth, which is particularly true when the dust size power
exponent $q$ is $q=2.5$. On the other hand, the decrease is less pronounced
when the dust size power exponent $q$ is $q=3.5$, i.e., when the small dust is
also responsible for the dust cross-section. Our results suggest that detailed
dust coagulation and fragmentation processes play a vital role in the magnetic
resistivities in protostar formation.
