In Niger, onion production has grown but the unsuitability of fertilization techniques and application of fertilizer doses are challenges to be met in order to improve onion yield. This study aims to assess the effects of mineral (NPK) and organic (compost) fertilizers on the productivity of «violet de Galmi» onion (Allium cepa L.). The study is carried out at the Saga experimental site (Niger). The experimental design used is a completely randomized block consisting of three repetitions and six treatments including a control treatment (T0). The treatments are: T0 (300kg/ha of NPK + 20t/ha of compost); T1 (200kg/ha of NPK); T2 (100kg/kg of NPK + 20t/ha of compost); T3 (300kg/ha of NPK + 10t/ha of compounds); T4 (300kg/ha of NPK + 5t/ha of compost); T5 (300kg/ha of NPK + 15t/ha of compost). The results of the study showed that the plots having received the treatments T5, T4, T3 and T0 recorded numbers of superior bulbs respectively of 29,333 bulbs, 33.67 bulbs, 34 bulbs and 35.67 bulbs. And that the yields of biomass (5.57±1.84t/ha) and bulbs (30.00±5.00) recorded for the T0 treatments are part of the low yields recorded in the study. The dose of fertilizers in treatment T2 provided a significantly high yield (31.67±3.63). The results obtained at the end of this study show the interest in using organic matter as fertilizer in onion growing systems, in order to increase soil productivity and ensure their sustainable exploitation.