This study investigates the effects of sea-land breezes (SLBs) and northeastern monsoon (NEM) on the physicochemical properties of particulate matter (PM) in the atmosphere over southeastern coastal region of Taiwan Strait. The intensive PM sampling protocol was consecutively conducted for forty-eight hours. During the sampling periods, PM2.5 and PM2.5–10 were simultaneously measured with dichotomous samplers at four sites (two inland and two at offshore sites) and PM10 was measured with beta-ray monitors at these same four sites. Strong SLBs were regularly observed in the coastal region of southern Taiwan during the SLBs periods, while significant northeastern monsoons appeared during the NEM periods. The mass ratios of PM2.5/PM10 during the NEM periods were always higher than the SLBs periods. The most abundant ionic species of PM were SO42-, NO3-, and NH4+. The most common chemical compounds of PM in southern Taiwan were ammonium sulfate ((NH4)2SO4) and ammonium nitrate (NH4NO3). Carbon contents of PM during the NEM periods were higher than during the SLBs periods. The organic-to-elemental-carbon ratio (OC/EC) of PM2.5 ranged from 1.05 to 4.39 with an average of 2.26. The order of major metallic elements of PM2.5 in the SLBs and NEM periods is Fe > Ca > K > Al > Mg > Zn > Pb and Ca > Fe > Al > K > Mg > V > Ni, respectively, and of PM2.5–10 is Ca > K > Al > Fe > Mg > Zn and Fe > Ca > Al > K > Mg > V > Ni, respectively. This study reveals that the accumulation of PM offshore, due to land breezes, influences the tempospatial distribution of PM at the coastal region in southern Taiwan. Moreover, the nss-[SO42-]/[Na+] ratio regarded as a PM pollution index, is more suitable than the [NO3-]/[Na+] ratio.