An investigation was carried out with paclobutrazol (Bonzi), daminozide (B-Nine) and chlormequat chloride (Cycocel) in order to study their effect on control of elongation in cucumber seedlings. The seeds of cucumber cv. 'Maraton F-1' were soaked into 500 and 1000 mg/L solutions of paclobutrazol, and 7500 and 15000 mg/L solutions of daminozide and chlormequat chloride, each for 12 and 24 hours. After soaking the seeds were sown into peat medium in which the plants were grown for 20 days in a greenhouse. Measurements of height and quality of seedlings were measured from control and treated seedlings. Paclobutrazol applications were effective on seedling height, whereas daminozide and chlormequat chloride had lower inhibition. Both concentrations of paclobutrazol caused shortening in hypocotyl and epycotyl lengths. The transplant heights were reduced as 63.4% at 500 mg/L and 74.9% at 1000 mg/L. The application of paclobutrazol for 24 h showed effective seedling height control than that of 12 h. Paclobutrazol applications had no significant effect on stem diameter, however, decreased the leaf area and dry weight of both leaves and sterns. Applying daminozide and chlormequat chloride to seeds for 12 h was ineffective on plant height, while 24 h applications of 15000 mg/L daminozide and chlormequat chloride reduced the plant height.