Resistance of Cotton Germplasms Against Sucking Insect Pest, Amrasca biguttula (ISHIDA). IGAA. Indrayani and Siwi Sumartini. Morphological characteristics of cotton leaf have an important role on the resistance against sucking insect pest. Among the characters, leaf hair density is the most important in preventing the attack of sucking insect and it can be used to identify the resistance of cotton germplasms against sucking insect pest, A. biguttula. Study on resistance of cotton germplasms against sucking insect pest, A. biguttula (Ishida) was carried out at Asembagus Experimental Station of Indonesian Tobacco and Fiber Crops Research Institute (IToFCRI) in Malang from January to December 2009. The objective of study was to find out resistant cotton germplasms to A. biguttula. Fifty accessions of cotton germplasm were used as treatment and arranged in Randomized Block Design (RBD) with three replications. Plot size used was 10 m x 3 m that consists of two rows of tested accession and one row of Tamcot SP 37 as an atractant plant for A. biguttula. Parameters observed were leaf hair density, length of hair, population of A. biguttula nymph, and plant damage. Cotton accessions with higher hair density and length of leaf hair significantly reduced the frequency of action threshold population of A. biguttula and plant damage. Eleven cotton accessions, viz., SATU 65; VAR 78443; Sukothai 14; GM5U/4/2; Samir 730; L1; L4 x Rex/1; Paymaster 404; ISA 205B; Albar 72B; dan Tashkent 2 were showed more resistant to A. biguttula because of higher leaf hair density (121-360 hairs/cm2), lower nymph population (0-2 times of population threshold) and lower damage score (1.0-1.8). These cotton accessions could be promising to be genetic resources of resistance to sucking insect pest, A. biguttula.