Carlitz and Riordan introduced the q-analogue fq(n,k)of ballot numbers.In this paper,using the combinatorial interpretation of fq(n,k)and constructing injections,we prove that fq(n,k)is q-log-concave with respect to n and k,i.e.,all coefficients of the polynomials fq(n,k)2-fq(n+1,k)fq(n-1,k)and fq(n,k)2-fq(n,k+1)fq(n,k-1)are non-negative for 0＜k＜n.
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