Yes, you are supposed to use both serums at the same time, however, do not mix them in the palm of your hand. After cleansing and exfoliating the skin, (exfoliation is to be done at least twice a week), you will apply the Vitamin C Serum first, and allow to dry for several minutes. Next, apply the Hyaluronic Acid Serum and allow to dry for several minutes, and lastly apply your moisturizer and eye treatment. Also, nighttime is the best time for use, as skin repairs itself while you sleep.