Two field experiments were conducted at Sakha Agricultural Research Station, Kafr El-Sheikh Governorate during 2002 and 2003 seasons to study the response of Giza 88 cotton cultivar to two sowing dates at early sowing (25^th March) and late sowing (5^th May) and thinning dates were at three physiological ages; i.e. when cotton plants formed the first true leaf, the second true leaf and the third true leaf. A split plot design was used with four replications. The obtained results revealed that early sowing (25 March) significantly increased number of internodes and sympodia on the main stem, number of open bolls per plant, boll weight, number of days to the first flower appearance, days to the first cracking boll, earliness percentage and seed cotton yield, per plant and feddan while the reverse trend was noticed with plant height, internode length number of monopodial branches and first sympodium position. On the other hand, earliness measurements, such as position of first sympodium, days to first flower appearance and cracking boll and earliness percentage were significantly increased when cotton plants were sown early in the season. Also, the early sowing date (25^th March) produced the highest value of open bolls, boll weight, seed cotton yield /plant and feddan, while number of unopen bolls/plant, seed index and lint percentage were not significantly affected by sowing date. On the other hand, thinning date significantly affected the growth traits, earliness parameters, yield and its components in the two seasons except number of unopen bolls/plant, seed index and lint percentage. Thinning conducted when cotton plants formed the second true leaf gave the best result in the two seasons. Delaying thinning date significantly increased plant height, the internode length, position of first sympodium, days from sowing to appearance of the first flower and cracking the first boll while, the reverse trend was true for number of internodes on the main stem, number of monopodia and sympodia/plant, earliness percentage, number of open bolls/plant, boll weight, lint % and seed cotton yield/plant and feddan.                 The interaction had insignificant effect on all traits studied except number of unopen bolls per plant, seed index and lint percentage.                 Generally, best results were obtained when cotton plants were sown early (25^th March) and thinned after formation of the second true leaf.