The purpose of the present study was to investigate the synthesized study on Piaget's conservation. To examine the above purpose, the three experiments were conducted. 1) To clarify the process of acquisition of conservation tasks and the correlation of them.(Experiment I: Conservation Test) 2) To check the accelerative extent of conservation which was acquired by the training through the cognitive conflict trials.(Experiment II: Training of Conservation) 3) In order to compare the concept of conservation acquired by training and that of the natural condition, the extent of the resistance to extinction was examined.(Experiment III: Extinction of Conservation) Methods: Experiment I, 286 children (3: 6-to-8: 5-years old) were given 37 tests, which consisted of seven kinds of conservation tasks, i. e. substance, liquid, number, weight, length, area 1 and area 2. Experiment II, 129 non-conservers were given cognitive conflict by the operation of addition, subtraction and transformation. Namely, after the operation of addition or subtraction, the materials were transformed, and by the operation of the transformation, big material seemed small, and small one seemed big. In the training were included 37 tests which consisted of six kinds of conservation tasks, and each test was repeated twice. To check the effect of the training, a posttest which was same as Experiment I was administered. Experiment III, 96 conservers, in which two kinds of conservers were included ; one by training and the other by the natural condition, were tested the extinction of conservation consisted of number, weight, length and area.(total test numbers were 16) After the extinction, Ss were given 15 conservation tests that were selected from the Experi ment I. Results: 1) In Experiment I, conservation of substance, liquid, number and length was mastered by the age of eight, and the conservation of weight came next. The conservation of area appeared a year later, The results showed that seven kinds of conservations were attained almost at the same period. This finding indicates that once the reversible operation is completed, it can be applied to the other conservation tests. 2) The correlation coefficients among seven conservation tasks were very high. Ss who get a full mark in one conservation test also get high marks for other tests. 3) According to the results of two kinds of factor analysis, i. e. the principal axis method and the varimax method, it was shown that a common factor (conservation factor) was extracted. Conservation of area and weight showed somewhat different components compared with other conservation tasks. 4) The training of conservation gave positive effects on children. 5) In the Experiment III, almost all the Ss indicated resistance to extinction. From this, the concept of conservation acquired by training was essentially the same quality as that of acquired naturally.