To assess the effect of floor levels of high-rise apartment buildings on the accumulation of contaminants in indoor environment, residential air-conditioner filter dust (ACFD) samples from the 1st, 10th, 20th and 30th floors of a high-rise apartment building were collected for the determination of n-alkanes and polycyclic aromatic hydrocarbons (PAHs). The results show that both n-alkanes and PAHs in the residential ACFD were ubiquitous but varied greatly in concentrations. The total concentrations of 27 n-alkanes (Σ27AK) and 16 PAHs (Σ16PAH) ranged from 1.35 to 9290 µg g–1 and 278–34200 ng g–1, respectively. Source apportionment revealed that n-alkanes were from mixed sources combining fossil fuel combustion, natural emission and solid biomass burning, but PAHs were mainly from indoor sources. Furthermore, the diagnostic ratio of paired low weight molecular PAH species may change during transportation and accumulation. Significantly higher concentrations of Σ27AK and Σ16PAH were observed in the samples from low floor levels (the 1st and 10th floors) compared to those from high floor levels (the 20th and 30th floors). The results of classification and regression tree analysis clearly suggested floor level is the most important factor influencing the accumulation of Σ27AK and Σ16PAH in the ACFD. Our findings imply that people living on lower floor levels have greater exposure risks to PAHs associated with indoor dust.