This study. was aimed at investigating the relation of intelligence to concept learning. Two experiments were undertaken to clarify how different was the effct of task cclnplexity and intuitiveness. of the relevant dimension on learners' performance, depending on their intellectual development. In both experiments, Ss were to learn a simple concept which was defined by a value on a certain dimension. Ss were presented instances one at a time and required to bauess whether it belonged to concept A or not. Confirming information was given immediately. Successive 10 correct responses were required as the criterion of learning. An instance could be described by values of 3 (form and number of Ligures, and width of a border) or 6 climension, (color of figure, color and position of a border in addition to 3 dimensions described above). Experimental variables were i) number of irrelevent dimensions' (2, 5) and ii) intuitiveness of the relevant dimension (intuitively conspicuous---form of figures, intuitively less noticiable---width of a border).