Warp yarn tension is the most important factor that affects weaving performance and fabric property. In this study the influence of warp tension on the properties and efficiency of denim twill fabric on Toyota®air jet loom (Dobby shedding) at Kanoria® Africa denim producing company has been investigated. The yarn used was cotton yarn of 7Ne for both warp and weft. Ten different warp tensions were taken and selected properties of fabrics such as GSM, crimp, tear strength, breaking strength, abrasion resistance and breaking extension were tested. The end breakage and time taken to repair a single warp break were also studied, and then finally tested data was analyzed. The results showed that warp breaks were decreased to warp tension of 365 kgf beyond that it was increasing. The lower end breakage was 10.2 which obtained at warp tension 365 kgf at which a minimum end break was achieved. Statistical analysis of the results shows that in denim fabric, the variation of tension has significant influence on the breaking strength in the warp direction, breaking extension in warp and weft direction, tear resistance in weft and warp direction, crimp percentage in warp and weft direction and fabric weight. However it has no significant influence on abrasion resistance, count of thread, density of fabric and breaking strength in the weft direction.