This paper was summarized from the master's thesis of the first author (2015). Objectives: Purposes of the study are to compare the degree of change in horizontal and vertical handwriting size between idiopathic Parkinson's disease (IPD) patients with progressive micrographia and a control group, and to determine if vertical handwriting can reduce the severity of micrographia. Methods: Eleven IPD patients who were at Hoehn and Yahr (H&Y) stages 2 and beyond with progressive micrographia were matched to a control group by such factors as age, gender, educational background and handedness. The tasks included horizontal as well as vertical writings of a palindrome ("yeobogejeogijeogeboyeo") and a single-syllable sequence ("bobobobobobo"). Results: In the PD group, upon writing vertically, the handwriting size of the whole phrase, of one syllable, and of 3-syllable words in palindrome was significantly larger in comparison to the horizontal handwriting. Similarly, in case of the single-syllable sequence, the vertical handwriting size of the whole sequence, of one syllable, and of 3-syllable words was found to be significantly greater in comparison to horizontal writing. Conclusion: Vertical writing instead of horizontal writing may help IPD patients to overcome micrographia. In the absence of external cues (e.g., parallel lines, square grids, auditory cues), vertical writing would assist the patients in maintaining a constant handwriting size in their daily lives.