This study revised the theory of planned behavior (TPB) by incorporating the new concepts of gambling passion and responsible gambling strategy (RGS) to predict gamblers’ intention to gamble in online sports betting. The data were collected at the end of March in 2012 through an online gambling website. The findings indicated that the inclusion of two types of gambling passion and two types of RGS explains online gambling intention well. Specifically, out of the original antecedent predictors of TPB, attitude toward online gambling was positively related to harmonious passion. Subjective norm had a positive relationship with both harmonious and obsessive passion. The results also showed that perceived behavioral control does not have a significant effect on the two gambling passions but has a direct and significant influence on behavioral intention. Additionally, the compulsory RGS had a negative effect on obsessive passion, whereas supplementary RGS had concurrent positive impacts on harmonious and obsessive passion. Lastly, the two gambling passions were notable predictors of behavioral intention toward online sports betting.