Com is planted in two seasons per year in northern Iran (mid-April as a main crop and mid-June as a second crop after wheat harvest). Therefore this study was to determine if com growth and yield would differ between these two seasons, as well as to different planting densities. Two field experiments were conducted with a Randomized Complete Block Design on 19 th April (as a main th O \\\' crop) and 18 June (as a second crop) in Agricultural Research Center of (Golestan-Iran) (36 53 N, 54° 2i\\\' E) in 2008. Each experiment included 7 planting densities (1600, 25000, 45000, 65000, 85000, 105000 and 125000 plants ha- 1) with four replications. Each plot contained 4 rows with 7 meters in length. Distance between rows was 0. 75 m. Both experiments were conducted without any water and nutrient limitation. Phonological traits measured were emergence date, tasseling, silking, milk stage, dough stage, physiological maturity and harvesting time were recorded during the growth stages. To analyze the data a combined analysis ANOV A was done. Least significant differences test (LSD) was used to compare the mean values in each trait. The results showed that the effect of planting densities and season were significantly different in most traits. The values of total dry matter (TOM), grain yield, ear length , ear per plant, W 1000, stem diameter, harvest index, seed number per rows, (cob+ husk) weight, (cob+ husk)% in first season were significantly higher than second season (between 6.5% and 52.7%), but the percent of stem weight in second season was more than first season by (29.1 %). ANOVA showed a significant interaction between season and density for 12 of 14 properties (TOM, stem weight, grain yield, ear length, ear per plant, stem diameter, seed number per rows, number of seed row, (cob+ husk) weight, (cob+ husk)%, harvest index) . In first season maximum values of, TOM , stem weight, and stem % observed in middle densities (65000 and 85000 plants ha-1) while in second season their maximum value observed in high planting densities 105000-125000 plants ha-1) . Maximum grain yield observed in middle planting densities in first season while in second season the grain yield was same in planting densities between 25000 and 125000 plant ha-1• The low values in growth parameters for the season two was due to the higher temperature in season two than season one (in first season 14 days during growth stages experience temperature more than 34°C while in second season maximum temperature in 38 days was more than 34°C) hence maize grown in season two had a shorter growing period (days to maturity in first season was 105 days while in second season it was 100 days). Exponential function was fitted to show relationship between yield per plant (Y) and planting densities (X) (Y = 416.22 x exp-0 14 6 x, R 2 = 0.987) and (Y= 229.39 x exp-0· 141 x, R2 = 0.954) were the developed equations for first and second season respectively. Although the yield per plant in two season was not same but the equations showed that the slope of curves in both seasons were fallowed nearly a same trend (-0.146 and -0.141) it means the intensity of yield reduction with increasing plant density was similar for both seasons. This study found that com should be planted in season one for higher com growth and yield.

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