Bio-stimulants are formulated product of biological origin that improves plant productivity as a consequence of the novel or emergent properties of the complex of constituents. This study investigated the potential of bio-stimulant and potassium sources to improve the performance of cotton. The current study comprised of cotton cultivars i.e., CIM-573 and CIM-598, foliar spray of bio-stimulant (Moringa Leaf Extract) (MLE) alone and combined with potassium nitrate (K=2%, N=0.57%), muriate of potash (K=2%, Cl=1.5%) and potassium sulphate (K=2%, S=0.72%) keeping tap water spray as a control. The experiment was laid out in a Randomized Complete Block Design (RCBD) with factorial arrangement on a silt loam soil. Field study was conducted at Osmania Agricultural Farm, Shujabad (29.7686 °N, 71.3283 °E; 152 m asl) and Agronomic Research Area, Bahauddin Zakariya University, Multan (30.2639 °N, 71.5101 °E; 123 m asl), Pakistan during 2013. Results revealed positive effect of exogenously applied bio-stimulant and various potassium sources on the growth, yield and fiber quality of cotton cultivars at both sites. However, combined application of MLE and potassium nitrate produced significantly higher absolute and relative growth rate, leaf area index, number of green bolls, seed index, cotton seed and lint yield of Bt while plant height, fiber maturity and uniformity ratio in conventional cotton cultivar. Therefore, the present study suggests that foliar spray of MLE alone and in combination with potassium sources could be used to improve the productivity and quality of cotton. Exogenous application of MLE has a great effect on photosynthetic and enzymatic activities that appropriate the efficiency of utilizing nutrients and thereby its combined application with potassium nitrate improve the growth and seed cotton yield and quality characters in cotton.