Chronic impairments of brain caused by accumulation of endogenous formaldehyde as ageing is thought as one of the risk factors for sporadic age-related dementia. Thus, it is necessary to determine the endogenous concentration of formaldehyde in brain. Using 2, 4-dinitrophenylhydrazine (2, 4-DNPH) in the assay, the concentrations of formaldehyde in parietal lobe, frontal lobe, temporal lobe, occipital lobe, hippocampus, cerebellum and brainstem of porcine brain (n=5) were measured through UV-HPLC. Homogenizing brain tissues with 10% trichloroacetic acid (pH=1.0) not only avoided the disturbance from contaminated protein and other compounds, but also eliminated the step extraction of FA-DNPH derivative (2, 4-dinitrophenylhydrazone) and improve the methodological sensitivity (P < 0.05). The porcine brain formaldehyde was 75.5～83.4 μmol/kg fresh brain tissues measured by this improved method. Recoveries of spiked formaldehyde at low and high level were 95.96%～102.04% with relative standard deviations less than 10%. This suggests that the modified 2, 4-DNPH method is effective enough to measure the endogenous formaldehyde in brain tissues.