What role do the magnitudes of the constituent digits play in three-digit number comparison (e.g., choosing the larger one of two numbers)? The present study addressed this question by examining compatibility effects between hundred and decade digits and between hundred and unit digits. For example, the number pair 372-845 is hundred-decade incompatible because the larger number contains the smaller decade digit, but hundred-unit compatible because the larger number contains the larger unit digit. We obtained significant effects of hundred-decade and hundred-unit compatibility on number comparison times. However, the effect of hundred-unit compatibility was largely restricted to the hundred-decade-compatible condition. These results suggest that place-value information, through decomposition, is automatically taken into account when multidigit numbers have to be compared. Implications of our findings for models of number processing are discussed.