This study was conducted to test the reliability and validity of "What my baby is like(WBL)" that was developed by Pridham et al. for measuring infant temperament. 37 subjects were participated four times-1, 3, 6, and 12months, and 146 cases were analyzed. The construct validity for the scale was tested by factor analysis with four factor loading solution based on the previous study. One item was excluded because total-item correlation was too low, so that the number of total items were eighteen. The analysis yielded four well defined factors: amenability and persistence, activity, reactivity, and adaptability. These four factors explained 57.62% of the variance in the infant temperament. The criterion related Validity was confirmed by the relationship between the infant temperament and HOME, and between the infant temperament maternal confidence in childrearing. The reliability of the scale was determined with Cronbach's alpha coefficient and Guttman split-half coefficient. Cronbach's alpha was .86, for 18 items, and Guttman split-half cofficient was .81. In subscale analysis, Cronbach's alpha was .56~.84. In conclusion, WBL showed a high degree of validity and reliability, suitable in Korean infants for measuring temperament. In the further study, it would be necessary to refine the concept of temperament and to analyze the correlation between WBL and other temperament inventory.