The formation of self assembled CdSe quantum dots under Stranski Krastanow (S K) mode by low pressure metalorganic chemical vapor deposition (LP MOCVD) was reported for the first time. The samples were grown directly on GaAs (100) surfaces by LP MOCVD. DimethylSelenide (DMSe) and DimethylCadmium (DMCd) were used as precursors. The growth pressure was kept at 2 93×10 4Pa and the growth temperature was 500℃. CdSe with the thickness of about 2 monolayers was grown directly on GaAs (100) surfaces. For the purpose of AFM observation, this uncapped sample was cooled down immediately to room temperature and was monitored under a Digital Instruments Nanoscope Ⅲa system at the same day of growth. The AFM images show that the average diameter, height and density of those self assembled CdSe quantum dots are 50±15nm, 13±4nm and 5μm -2 , respectively. And those dots’ diameter height ratio is about 4～5, just the same as those results observed in other Ⅱ Ⅵ and Ⅲ Ⅵ compounds which were grown under S K mode by MBE. The formation of self assembled CdSe quantum dots under Stranski Krastanow (SK) mode by low pressure metalorganic chemical vapor deposition (LP MOCVD) was reported for the first time. The samples were grown directly on GaAs (100) surfaces by LP MOCVD. DimethylSelenide ( DMSe) and DimethylCadmium (DMCd) were used as precursors. The growth pressure was kept at 93 × 10 4 Pa ​​and the growth temperature was 500 ° C. For CdSe with the thickness of about 2 monolayers was grown directly on GaAs (100) surfaces. For the purpose of AFM observation, this uncapped sample was cooled down immediately to room temperature and was monitored under a Digital Instruments Nanoscope IIIa system at the same day of growth. The AFM images show that the average diameter, height and density of those self assembled CdSe quantum dots are 50 ± 15 nm, 13 ± 4 nm and 5 μm -2, respectively. And those dots’ diameter height ratio is about 4 ~ 5, just the same as those results observed in other Ⅱ Ⅵ and Ⅲ Ⅵ compounds which were grown under S K mode by MBE.