Magnitudes of numbers influence numerical inequality judgments of people. Do symbols representing numbers also affect numerical inequality judgments? To answer the question, I manipulated digit similarity in two-digit number comparison tasks. During the experiment, the participants took part in two comparison tasks – the judging-larger task and the judging-smaller task. Given pairs of two-digit numbers, the participants were required to make numerical inequality judgments (judging larger or judging smaller). To investigate the effect of digit similarity, two kinds of number pairs were used. Two-digit number pairs consisting of same-digits numbers (e.g., 21 – 12) and two-digit number pairs consisting of different-digits numbers (e.g., 21 – 30) were presented at random. The participants needed more time to compare the same-digits number pairs than the different-digits pairs. The result was independent of the findings in number comparison studies such as the numerical-distance effect (Moyer & Landauer, 1967) and the unit-decade compatibility effect (Nuerk, Weger, & Willmes, 2001). The present study poses challenge to the current theories of two-digit number comparison.