Abstract: The milk line is an important indicator for the determination of the degree of maize maturity. To know the effect of irrigation and nitrogen on milk line development of maize seed, a field experiment involving two maize genotypes (‘ZD958’ and ‘XY335’) was conducted. The experiment included three irrigation treatments (copious irrigation, 6 000 m³·hm^-2, W₆₀₀₀; moderate stress irrigation, 4 500 m³·hm^-2, W₄₅₀₀; and severe stress irrigation, 3 000 m³·hm^-2, W₃₀₀₀) and three levels of nitrogen application no nitrogen application, 0 kg(N)·hm^-2, N₀; moderate nitrogen application, 225 kg(N)·hm^-2, N₂₂₅; and moderate-to-high nitrogen application, 450 kg(N)·hm^-2, N₄₅₀. The milk line development process, kernel moisture, 100-seed weight, dehydration rate and filling rate of maize seeds under different irrigation and nitrogen treatments were investigated. The results showed that milk line development of maize seeds of different varieties was significantly affected by different irrigation and nitrogen levels. Milk line development of ‘ZD958’ seed was 18–24 days and that of ‘XY335 was 33–36 days under different treatments. With increasing irrigation rate, milk line development of ‘ZD958’ seed was longer while that of ‘XY335’ seed was not affected by irrigation. There was no significant difference in seed moisture among treatments at the same stage of milk line development. The 100-grain weight of seed under nitrogen application treatments was significantly higher than that under no nitrogen application treatment. Also the dehydration rate of ‘ZD 958’ seed under severe stress irrigation was significant higher than that under other irrigation treatments. However, there was no difference in dehydration rates under different rates of nitrogen. Also the dehydration rate of ‘XY335’ seed was not affected by irrigation rate. There was no significant difference in filling rate of ‘ZD958’ seed under different irrigation rates. The filling rate of ‘ZD958’ seed under no nitrogen application and copious irrigation was significantly greater than that under nitrogen application. The filling rate of ‘XY335’ seed significantly increased with increasing irrigation rate. For the same irrigation rate, the filling rate of ‘XY335’ seed under moderate nitrogen application was significantly higher than that under other nitrogen rates. With 1% decrease in moisture of ‘ZD958’ seed, 100-grain weight increased by 0.37–0.88 g against that (0.43–1.34 g) for ‘XY335’ seed. Therefore, milk lime development of ‘ZD958’ seed was affected significantly by irrigation. The dehydration rate of seed increased with increasing stress irrigation application, resulting in relatively shorter milk line development. Nitrogen significantly affected milk line development of ‘XY335’ seed. Also the filling rate of the seed was affected with short or excessive nitrogen application. This led to a relatively longer milk line development.