Fermentation conditions for natto-kinase production from solid-state Bacillus natto was optimized by using Plackett–Burman design, the steepest ascent design and response surface methodology in the study. The results showed that the main factors influencing natto-kinase production were initial moisture, fermentation time and temperature. The optimal conditions for natto-kinase production were at initial moisture of 90.24 g/(100 g) and fermentation time of 36 ℃ for 92.82 h by employing rapeseed meal as the solid substrate. The average activity of natto-kinase was increased to 6 031.33 IU/g in these conditions.