The purpose of this study was to uncover the factors that may influence K-3 in-service teachers' implementation of integrated curriculum (IC). To provide a consistent research base, the broad definition of IC and Jacob's model were adopted to clarify the controversial concept of IC. Survey data were collected from forty-two teachers from ten school districts in Ohio. Results showed that most teachers implemented IC on a regular basis; however, they preferred to use less integrated forms of the curriculum. In addition, the study revealed that though teachers overwhelmingly believed in the effectiveness of IC and their own knowledge and skills on IC, their agreement levels about other factors that might affect IC implementation varied. Teachers' planning time and compatible working hours with their colleagues were identified as the significant predictors affecting teachers' frequency of using IC. Community support, colleague support and teachers' knowledge and skills of implementing IC were found to moderately influence the form of IC most frequently adopted by those K-3 teachers. Educational implications and recommendations for future research are discussed.