  General formula for symmetry factors (S-factor) of Feynman diagrams
containing fields with high spins is derived. We prove that symmetry factors of
Feynman diagrams of well-known theories do not depend on spins of fields. In
contributions to S-factors, self-conjugate fields and non self-conjugate fields
play the same roles as real scalar fields and complex scalar fields,
respectively. Thus, the formula of S-factors for scalar theories --- theories
include only real and complex scalar fields --- works on all well-known
theories of fields with high spins.Two interesting consequences deduced from
our result are : (i) S-factors of all external connected diagrams consisting of
only vertices with three different fields, e.g., spinor QED, are equal to
unity; (ii) some diagrams with different topologies can contribute the same
factor, leading to the result that the inverse S-factor for the total
contribution is the sum of inverse S-factors, i.e., 1/S = \sum_i (1/S_i).
