Recent developments of quantitative analyses for explorations of changes in writers' mental condition, emotion, and thought have attracted much attention. Here, we report a quantitative approach for estimating ‘the possible time of the literature style evolution in Koji Uno’s works’. Koji Uno, a well-known Japanese litterateur, suffered mental illness in 1927 and stopped his writing about 6 years because of the disease treatment and recovery. It was reported that his literature style changed when he restarted his writing after recovering from the illness. However, the work named ‘Nichiyobi’ which had been published before the disease treatment is much more similar with the works written after recovering. For understating the time of the literature style changed in Uno’s works, we studied four features in the published writings of Uno before the illness using discrimination analysis method, which suggested that the writing style has been changed before the disease treatment.