Egypt is key producer and exporter of dry onion globally. One of the best performing varieties in Upper Egypt that is very desirable for exportation is Giza 6 Mohassan. However, local farmers producing the seeds of this variety often do not follow proper seed production practices, leading to increased bolting (premature flowering) and bulb doubling over time. This investigation examines the efficacy of mass selection practiced by farmers against bolting and bulb doubling in improving onion bulb quality of Giza 6 Mohassan and also, to test the effect of NPK level on the newly selected genotypes. Two cycles of mass selection as practiced by   farmers were applied to locally produced Giza 6 Mohassan (base population) collected from farmers' fields. Our results showed that mass selection decreased inside doubling by 4.45% and 7.9% in the first and second cycles, respectively, and overall, by 12% over two cycles. Outside doubling was reduced by 12.1% in first cycle and by 34% in the second cycle, with an overall decrease of 34.41% over two cycles. Bolting was reduced by 44.1% and 15% in the first and second cycle, respectively, with a total reduction of 53.94% over two cycles. High levels of NPK reduced bolting but increased bulb doubling, while also increasing yield and marketable yield. These findings indicate that mass selection significantly improves onion bulb quality and reduces bolting and doubling rates. High NPK enhances yield, but it needs to be managed accurately to avoid increasing bulb doubling.