The increase of carbon dioxide (CO2) has been identified since the industrial revolution era. Albizia saman is a tree species which can absorb excess CO2 from the atmosphere in large quantities. This study was to identify the effect of spraying time and concentration of paclobutrazol on the growth of A. saman seedlings. This research using a completely randomized design, the first factor is spraying time which is divided into three levels: spraying at age of 25, 50 and 75 days. The second one is the concentration of paclobutrazol, consisting of four levels: control, 75, 150 and 225 mol·L-1. The further test used are DMRT at p<0.05. Paclobutrazol influences the higher rate of photosynthesis, namely 38.27 M CO2 m-2s-. There are varied stomatal conductance values, where the highest value is 0.35 mM m-2s-1 and the lowest carbon dioxide content in treatment is 56.86 mol·L-1. The slowest transpiration rate is the combination of 50 days after treatment, and the concentration of paclobutrazol is 0.24 mM H2O m-2s-1. The shortest growth of A. saman is shown from the 50-day treatment using paclobutrazol and 150 mol·L-1 concentration. The relationship between photosynthetic rate and stomatal conductance and transpiration concludes that the trend is similar to that of the curve, whereas the trend is not the same as the internal CO2.