Abstract: ‘Ershuizao’garlic was used as experimental material to investigate the effects of different photoperiod treatment on the enlargement and nutritional quality of garlic bulb. The results indicated that the 14 h（7 h natural light + 7 h artificial light）uninterrupted illumination was necessary for garlic bulbing enlargement. However，under 7 h natural light，all supplements of light from 1 h to 7 h to break darkness at night could increase the bulbing enlargement more quickly than continuous 14 h illumination treatment. The difference of bulb weights among treatments of darkness break（1 - 7 h）was not significant. With the extension of light supplying at night（1 - 7 h），contents of leaf pigment，allicin，soluble sugars，vitamin C，soluble proteins and free amino acids of bulb were increased first and then decreased，and the treatment of 5 h darkness break showed the highest levels of pigment，vitamin C，soluble proteins and freeamino acids content in the bulb，which is about 30.0%，7.7%，36.2% and 25.3% higher than 14 h uninterrupted illumination，respectively. Furthermore，both the content of total phenol and the free radical scavenging rate also showed the highest level in the treatment of 5 h darkness break. If the main purpose of protected garlic production was to get the yield，1 h darkness break treatment was enough，if both yield and quality were considered，5 h darkness break was the proper treatment.

Key words: garlic, photoperiod, break the darkness, bulb, nutrient quality