a b s t r a c t Agbeko (1986) [5] proved some concave function inequalities for sub-(super-) martingales.Christofides (2003) [3] obtained some maximal inequalities for concave Young functions for N-demimartingales. In this paper, we will further extend these results to the cases of demimartingales and N-demimartingales. Our results also generalize and improve partial results of Wang et al. (2010Wang et al. ( , 2011.