The purpose of this study was to investigate the effect of length measuring activity using nonstandard units on young children s ability to measure length and mathematical attitude. Findings of this study were as follows: First, there was a significant difference of young children s ability to measure length between the experimental group which was treated with the length measuring activity using nonstandard units and the control group which was not treated (p < .05). Specifically, young children s ability to measure length with direct comparison showed no significant group difference, but their ability to measure length using nonstandard units showed a significant group difference (p < .05). Second, there was a significant difference of young children s attitude toward mathematics between the experimental group which was treated with the length measuring activity using nonstandard units and the control group which was not treated (p < .05).