This study aimed to explore the gender-based seasonal patterns of suicide in Japan between 2005 and 2012. With data from Japanese official reports, we carried out Prais–Winsten regression and Wilcoxon signed-rank test analysis with Stata 12.0 and SPSS 14.0. The suicide number was significantly higher in March, April, May, June, July, and October for both genders. The suicide number in men was markedly higher than that in women in every month. The suicide number in 2010 was lower than that in 2009 for men, while that in 2011 was higher than that in 2010 for women. The findings displayed that the nationwide television and publicity intervention campaigns might have positive effects on decreasing suicide of men while women suffered a post-earthquake increase. In terms of interventions, we should not only square up the seasonal patterns but also the gender differences in vulnerability.