Two production tests were conducted to investigate the effects of input-frequency and property of rules for negative forms of Japanese language, using real and nonce words. The subjects were 10 untutored Japanese learners and 10 Japanese native speakers. ANOVA analysis showed significant differences between the high frequency words and the low frequency words in the learners' correct answers and the native speakers' reaction time. Also, suffix "-kunai" was found to be more correct than "-nai" and "-janai". In the nonce words test, both the learners and the native speakers preferred "-kunai" to "-nai" and "-janai" as a suffix when the word ends in the "i" sound. Also, the word which ends in the "ru" sound tended to be recognized as a verb. The results suggest that input-frequency and property of rules have some effects on the production of Japanese negative forms.