The present study was undertaken in Technology, Division, Cotton Research Institute, Agricultural Research Center Giza, seven Egyptian cotton varieties, were taken in the study, three extra-long staple varieties (Giza 45, Giza 88 and Giza 93), two delta long- staple varieties (Giza 86 and Giza 94), and two upper Egypt long- staple varieties (Giza 80 and Giza 90), grown in 2014-2015 season. To study the effect of the factor, the relative importance and the contribution of spain length at 2.5% (SL 2.5% mm (X₁), spain length at 50% (SL 50% mm (X₂),  uniformity ratio (UR% (X₃), short fiber Content (SFC% (X₄), mean length (ML mm (X₅),  upper half mean length (UHM mm (X₆),  uniformity index (UI% (X₇), spain length at 66.7% (SL 66.7% mm (X₈), coefficient of variation length (C.v% (X₉), micronaire reading (Mic (X₁₀), fiber strength in gram/Tex (Str. g/tex (X₁₁),  fiber elongation (Elon.% (X₁₂), maturity ratio (MR% (X₁₃), and neps formation (neps cnt./g). in cotton yarns. From the path coefficient analysis, it was concluded that Micronaire reading was the most important causative factor inducing neps in cotton yarns. In fact, Micronaire reading exerted influence both directly and indirectly upon neps count. Fiber length showed a moderate effect, while fiber stiffness revealed the lowest effect on yarn neps count compared with the other two factors.