Poverty is a major determinant of population health, but little is known about its role in modifying air pollution effects. We examined whether people residing in socially deprived communities are at higher mortality risk from air pollution. This study included 209 tertiary planning units (TPU), the smallest units for town planning in Hong Kong. The socioeconomic status of each TPU was measured by a social deprivation index (SDI) derived from the proportions of unemployed population, monthly household income<US$250, no schooling, one-person household, never-married status, and subtenancy, from the 2001 Population Census. TPU were classified into three levels of SDI: low, middle, and high. Time-series analysis with Poisson regression was used to examine the association between changes in air pollution level and number of deaths in each SDI group in 1996-2002. NO2, SO2, PM10 and O3 were assoicated with all natural causes and cardiovascular mortality in middle or high SDI areas. All natural causes and cardiorespiratory mortality in high SDI areas were more strongly associated with SO2 and NO2 compared with those in middle or low SDI areas. We concluded that neighborhood socioeconomic deprivation increases mortality risks associated with air pollution.