Abstract. For certain two cases of splitting behaviors of the prime at infinity with unit rank r, given positive integers m, n, we construct infinitely many global function fields K such that the ideal class group of K of degree m over F(T ) has n-rank at least m − r − 1 and the prime at infinity splits in K as given, where F denotes a finite field and T a transcendental element over F. In detail, for positive integers m, n and r with 0 ≤ r ≤ m − 1 and a given signature (e i , f i ), 1 ≤ i ≤ r + 1, such that r+1 i=1 e i f i = m, in the following two cases where e i is arbitrary and f i = 1 for each i, or e i = 1 and f i 's are the same for each i, we construct infinitely many global function fields K of degree m over F(T ) such that the ideal class group of K contains a subgroup isomorphic to (Z/nZ) m−r−1 and the prime at infinity ℘ ∞ splits into r + 1 primes P 1 , P 2 , · · · , P r+1 in K with e(P i /℘ ∞ ) = e i and f(P i /℘ ∞ ) = f i for 1 ≤ i ≤ r + 1 (so, K is of unit rank r).