Purpose: The author compared monosyllabic Mandarin lexical tones produced by 3-year-old Mandarin-speaking children growing up in Taiwan and in the United States. Method: Following the procedures in Wong, Schwartz, and Jenkins (2005), the author collected monosyllabic tone productions from 3-year-old Mandarin-speaking children in Taiwan and low-pass filtered them to eliminate lexical information but retain tone information. Five Mandarin-speaking adults residing in Taiwan categorized these filtered tones and those produced by the Mandarin-speaking children growing up in the United States, the latter of which was reported in Wong et al. (2005). Agreements on tone categorization by judges residing in Taiwan and in the United States were evaluated. Tone accuracy of children growing up in Taiwan and the United States were examined and compared. Results: The Mandarin-speaking judges residing in the United States and in Taiwan showed high agreements on tone categorization. None of the 4 tones produced by the Mandarin-speaking children growing up in the United States and in Taiwan was adultlike.Children in Taiwan made more errors in Tone 2 and Tone 4 than did Mandarin-speaking children growing up in the United States. Accuracy rates of Tone 1 and Tone 3 were comparable in the 2 groups of children. Conclusion: Mandarin tone acquisition is a protracted process. Three-year-old Mandarin-speaking children growing up in Taiwan and the United States show similar developmental patterns and have not yet produced monosyllabic tones with adultlike accuracy.