A new adsorbent for formaldehyde extraction from aqueous solution was prepared using silica gel coated with polyethyleneimine. Silica gel was first modified with triethoxyoctylsilane, then polyethyleneimine was coated on the modified silica gel surface to improve the extraction efficiency and selectivity toward formaldehyde. The obtained adsorbents were characterized with thermogravimetric analysis, Fourier transforms infrared spectrometry and elemental analysis. The results showed that polyethyleneimine could be successfully coated on silica gel surface. In the coating step for 0.10 g of surface-modified silica, the suitable concentration of polyethyleneimine solution was 2% w/v (5 mL). And in the crosslink step, 1.0×10-7 M epichlorohydrin (3 mL) was used as crosslinking agent. The efficiency in formaldehyde extraction by the adsorbent was evaluated using batch method. The suitable pH for formaldehyde extraction was 4-9, using the extraction time of 120 minutes. The adsorption isotherm of formaldehyde on the adsorbent followed Langmuir isotherm with the maximum adsorption capacity of 25.9 mg/g. The desorption of formaldehyde from used adsorbent was achieved using 0.1 M hydrochloric acid with elution time of 5 minutes.