The implicit assumption of Piaget’s and Kohlberg’s cognitive developmental theory is the development of cognitive coherence (equilibrium between internal cognitive structure and external environmental world) via resolution of cognitive conflict. The present study aims to investigate whether the global coherence of moral thinking develops by age. The researchers utilized four moral scenarios to evaluate the participants’ responses to two contradicting arguments regarding behaviors of stealing, lying, cheating in an exam, and breaking a promise. The degree of coherence was evaluated by the correlation of the two responses. Since assessment materials should be developed differently for younger children and older subject, the researchers designed two separate studies for different age groups: Study 1 for elementary school children, and Study 2 for older subjects. Study 1 results showed that sixth graders’ moral judgment was more coherent than third graders’ except for the “Breading Promise” scenario. Study 2 showed that college students’ moral judgment was more coherent than sixth graders’ except for the “Breaking Promise” scenario, as well. Taking both Study 1 and Study 2 into account, coherence of moral thinking increases by age which supports Piaget and Kohlberg’s theoretical hypothesis.