In the years 2018-2021, experiments on the effect of air temperature and relative humidity (RH) on the storage of Welsh onion (Allium fistulosum L.) seeds were carried out. Three different cultivars and one breeding line received from commercial plant breeding and seed production companies were used. All their seeds at the beginning of storage had high germination over 90%, and moisture content 7-8%. Then, they were stored for 30 months in the controlled conditions at 3 different temparatures:  7-8 °C, 10 °C and 25 °C, each with 2 different air relative humidty (RH): 25% or 45%. During the experiment, their quality was evaluated by germination test according to the International Seed Testing Association (ISTA) protocol. Additionally, after 1 and 2 years of storage at 7-8 °C and 25% air RH, the seeds of the line were evaluated for their incidence of fungi. It was found out that seeds of the tested genotypes kept good germination at 7-8 °C and at 10 °C, i.e. after storing them, the same effect was achieved. Thus, the latter can effectively lower the costs of the seed storage in commercial seed trade of the crop. The electric current consumption for the seeds stored at 7-8 °C in comparison with 10 °C was higher by 11.2%. In seeds of 3 genotypes, after storing them for 30 months, their germination was better at the air RH 45% than at 25%. Generally, low temperature (7-8 °C) favoured growth of Penicillium spp. and Phoma spp. on Welsh onion seeds during 2 years of storage, while storing at higher temperature (25 °C) resulted in the increase in seed infestation with Cladosporium spp. and Fusarium spp. The results obtained from this research can be used as a guideline for the storage in climatic and RH controlled chambers of all genotypes belonging to Allium fistulosum species, with the aim to maintain its seed germination quality related to the duration of the storage and taking into consideration the operating energy costs.