A field trial was performed during 2015-16 to investigate the seed production potential of onion (variety Phulkara) under different potash (K) levels at SAU Tandojam using RCB design in three replicates having plot size of 5m x 3m (15m-2). Six treatments were formed including 0 kg ha-1control, 35 kg ha-1, 50 kg ha-1, 65 kg ha-1, 80 kg ha-1 and 95 kg ha-1. The growth and seed yield attributes of onion were significantly (P<0.05) affected by different K levels. The K at the rate of 95 kg ha^-1 produced 45.46 cm plant height, 3.77 umbels plant^-1, 147.17 seeds umbel^-1, 1.33 g weight of seeds umbel^-1, 890 g seed yield plot^-1 and 593.37 kg seed yield ha^-1. Similarly, K @80 kg ha^-1 produced 45.14 cm plant height, 3.75 umbels plant^-1, 146.11 seeds umbel^-1, 1.32 g weight of seeds umbel^-1, 884 g seed yield plot^-1 and 589.13 kg seed yield ha^-1. K application @65 kg ha^-1 resulted in 41.43 cm plant height, 3.44 umbels plant^-1, 134.12 seeds umbel^-1, 1.21 g weight of seeds umbel^-1, 811 g seed yield plot^-1 and 540.76 kg seed yield ha^-1. The lower K level of 50 kg ha^-1 resulted in 40.67 cm plant height, 3.38 umbels plant^-1, 131.63 seeds umbel^-1, 1.18 g weight of seeds umbel^-1, 796 g seed yield plot^-1and 530.74 kg seed yield ha^-1. The onion crop when given K only at the rate of 35 kg ha^-1 produced 38.36 cm plant height, 3.18 umbels plant^-1, 125.68 seeds umbel^-1, 1.13 g weight of seeds umbel^-1, 760 g seed yield plot^-1 and 506.72 kg seed yield ha^-1. However, in control (no potash) the crop produced 33.71 cm plant height, 2.80 umbels plant^-1, 113.18 seeds umbel^-1, 0.99 g weight of seeds umbel^-1, 677 g seed yield plot^-1 and 451.08 kg seed yield ha^-1. It was concluded that the differences in all the growth and seed yield attributes of onion under 80 kg and 95 kg ha^-1 potash levels were insignificant (P>0.05) suggesting that 80 kg ha^-1 K (as sulphate of potash) was an optimum K application rate in addition to 120 kg N and 100 kg P ha^-1 for achieving economically higher seed yield in onion variety Phulkara.