Different strains of cotton leafworm, Spodoptera littoralis larvae were collected from heavily sprayed fields or recently cultivated fields in different areas in Alexandria, and El-Boheira, proviance governorate. Chitinase activity was determined in laboratory susceptible strain of cotton leafworm and compared with enzyme activity for other collected strains which cleared that highest level of chitinase activity was found in Alexandria strains. The sensitivity of chitinase activity to chlorfluazuron and teflubenzuron was measured by I₅₀ values, values of I₅₀ in the case of chlorfluazuron were 0.23, 0.34, 0.41, 0.60, and 0.69 µM for lab strain; Borg El-Arab; West of Nobaria; Abou El-Matamir, and Edko strains of Spodoptera 2^nd larvae respectively, while I₅₀ values were 0.31, 0.40, 0.46, 0.66, and 0.74 µM for lab strain and four field strains of Spodoptera 4^th larvae respectively, similarly, the   teflubenzuron were 0.40, 0.50, 0.57, 0.74, and 0.82 µM for lab strain and four field strains of Spodoptera 2^nd larvae respectively, the I₅₀ values were 0.47, 0.59, 0.65, 0.88, and 0.93 µM for lab strain and four field strains of Spodoptera 4^th larvae respectively. Also, the inhibition constant (K_i) values were determined, the obtained data proved that compounds competitive inhibition of chitinase activity. The significant high mortality percentages were observed at all tested concentrations with chlorfluazuron than teflubenzuron and the result clearly showed that the 2^nd instar larvae were more sensitive to the compounds tested, compared to those of the 4^th instar, so when IGRs used for S. littoralis larvae control, dosage and timing of application should be carefully considered. The results of the present study may add some forward steps to use IGRs as alternative to conventional insecticides especially against this insect, so, the IGRs can be involved in important steps necessary for successful IPM programs applied against S. littoralis.