This research work was aimed at investigating play, as a mechanism for developing peaceful behaviour among elementary school pupils for sustainable peace in Cross River State, Nigeria. In order to determine this, Ex-post facto research design was used. Some determinants of play such as; playing age preference of pupils, gender differences and willingness to play with opposite sex and pupils' home background were identified as variables for the study. The population of the study was 26,363. A total of 200 primary six pupils formed the sample for the study through which the data were obtained, using purposive sampling technique. The instruments were faced validated and reliability ascertained. The data were analyzed using Pearson Product Movement Correlation Analysis (PPMCA) and Independent T-test at 0.05 level of significance. The result of the study revealed a significant relationship between playing age preference of pupils and their home background, between boys and girls exist no significant difference in their willingness to play with opposite sex.. The implication is that when pupils play together they develop peaceful behavior which will help the interact freely in their adult life leading to sustainable peace wherever they find themselves. Also, when pupils are allowed to play with their peers at home, they learn to tolerate others and develop peaceful behaviours. It was therefore recommended that Children should be allowed to play with their age mates and also with the ones of the same sex and opposite sex as this will help them to interact freely and also develop the social relationship that will bring about peaceful co-existence.