Generation of Ultrafine Bubble (UFB) on hydroponic culture solution has been reported to be able for stimulating the growth of plant. However, the promoting effect of UFB is still hard and inconsistent to be obtained due to the unknown optimum generation of UFB. Generation time of UFB influenced UFB concentration on hydroponic solution. Furthermore, the concentration of UFB have positive correlation with oxidative stress on plant that might affect the growth of plant. In this study, we aim to investigate growth response of lettuce to different UFB water treatment so that the optimum generation of UFB can be obtained. Fifteen seedlings were cultivated on a tray for 4 weeks. The cultivation was conducted at air temperature 20-23°C, relative humidity 60%-80%, under white LEDs that were adjusted at 200 ± 10 μmol·m-2·s-1 and irradiation cycle was set at 16h/8h (light/dark). Ten lettuces were harvested (1st Harvest) on 14th day and five lettuces were harvested (2nd Harvest) on 28th day. Air ultrafine bubble water was generated by UFB Generator (FZ1N-10 I, IDEC Corporation, Japan). UFB water was generated with 3 different generation time; 12 minutes (Gt1), 30 minutes (Gt2), and 120 minutes (Gt3). Generation time of UFB water was parallel with pass number. Pass number is the number of times the control water circulated entirely through the UFB generator. In this experiment, pass number were respectively 10 pass number (Gt1), 25 pass number (Gt2), and 100 pass number (Gt3). Each UFB water (Gt1, Gt2, and Gt3) were distributed respectively into 5 trays with different mixtures between UFB water and normal water as UFB water treatment (10% UFB water, 30% UFB water, 50% UFB water, 75% UFB water, and 100% UFB water). In addition, a tray with normal water was prepared as control treatment. Hydroponic solution was maintained at similar condition of DO, EC, pH, and temperature. The final result reconfirmed again the ability of air UFB water to accelerate the growth of lettuce on hydroponic solution. However, the excess or lack of UFB concentration did not significantly influence the growth of lettuce compared to control treatment. Since, the excess concentration of UFB might inhibit the growth of lettuce due to oxidative stress inside the plant. Moreover, lack concentration of UFB is not enough to stimulate the growth of lettuce. On the other hand, appropriate concentration of UFB significantly increased the fresh weight and dry weight of lettuce. The optimum growth of lettuce tended to shift into low concentration of UFB water when the generation time of UFB water is increased. In our experiment, the optimum growth of lettuce was obtained on 30% UFB water (Gt3) treatment and 75% UFB water (Gt2) treatment. Thus, this result illustrates how different generation of UFB will lead into different final result due to the important role of UFB concentration on the hydroponic solution.