An experimental study was conducted on the combustion and emissions characteristics of duel fuel sequential combustion (DFSC) mode on a single-cylinder engine, applying port injection of n-heptane combined with in-cylinder direct injection of commercial gasoline, ethanol and n-butyl alcohol, respectively. Three-stage combustion, which consists of low- and high-temperature combustion of premixed n-heptane and high temperature combustion of directly injected gasoline-like fuels were observed. The effects of the premixed ratio and overall heating values per cycle on the combustion characteristics and emissions were investigated. The experimental results show that: with the increasing of premixed ratio and overall heating values per-cycle, the ignition timing of the directly injected fuels advances and the maximum pressure and maximum mass-averaged temperature increase. Furthermore, the CO emissions increase to a peak point and then decrease with the increase of premixed ratio and overall heating values. While, it is very interesting to find that soot emissions achieve to an ultra-low level for DFSC with n-heptane/oxygenated fuels, particular with n-heptane/ethanol.