Abstract: The inductive effects of predatory rotifer Asplanchna brightwellii on morphological plasticity in four rotifer results showed that these four rotifer species cultured in the Asplanchna - conditioned medium had significant increase in the length of spines than in an ordinary culture medium, but there were no significant differences in the length and width of the body. The evolutionary and ecological significances of the morphological plasticity in four Brachionus species induced by the predators were discussed in the paper.