<b>A Study on Properties of Modified Rotor Spun Yarn</b> Fibers due to their large length diameter ratio are the most effective materials in supporting tensile loads still. Many textile applications do introduce fiber compressions either in a simple form or under complex loading conditions. The majority of these compressive loadings are directed laterally across the fiber axis like compression of fibrous assembly during draftee. Compression occurring to fabric during calendaring and embossing treatments etc. A special pre compression apparatus was fabricated and mounted before the entry of fibrous strand into opening roller of rotor spinning frame. Cotton Slivers were pre compressed in this zone at varying loads and the effect of this pre compression on the resultant yam has been studied. The yam properties considered for the study are the studies are U , tenacity, elongation, hairiness and imperfections. The drawback with rotor spun yams is lower tenacity and elongation which always need an improvement. Modified rotor spun yams obtained as a result of pre compression of slivers shows lesser U , reduced thin, dick and naps, lower hairiness values and mainly improved tenacity, elongation and work of rupture which would be a vital point for the industry. Fiber, Neps, Tenacity, Spun Yarn 653-658 Issue-5 Volume-2 K. Gopalakrishnan