Previous research mainly with monolingual children shows a positive relationship between English skills and emotion regulation. No study to date has examined if or how learning of grammatical morphemes might be associated with emotion regulation among bilingual preschoolers. This study examined how Mandarin-English bilingual preschoolers performed on three grammatical morphemes of plurals, past tense, present tense and whether the performance on the three morphemes was associated with emotion regulation. An elicitation task was used to assess proficiency in the three morphemes, and the Emotion Regulation Checklist (ERC) and the Disappointing Gift task were used to assess emotion regulation. The results indicate that Mandarin-English bilingual preschoolers had difficulties with all the three morphemes but they had a higher proficiency level on plurals than on past and present tense. Their proficiency in past and present tense was positively correlated with emotion regulation as measured by the ERC.