San Ysidro, the largest Land Port of Entry (LPOE) in the US with respect to pedestrian and vehicle traffic, is located at the very southern end of California, north of US-Mexico Border. Consequently, people of San Ysidro have high probability of exposure to fine particulate matter or PM2.5, and thus, experience higher risk of health burden. This study was designed for PM2.5 measurement in San Ysidro during summer 2017 and winter 2018 seasons. Four locations were selected: Nicoloff Elementary School, The Front Arte Cultura, San Ysidro Middle School representing near border region and Tijuana Estuary Visitor Center representing a coastal reference site. Two instruments were used in field sampling for PM2.5 mass measurement: DustTrak DRX for real time continuous aerosol measurement and MiniVol for gravimetric quantification using Teflon filter. Chemical analysis of PM2.5 mass was conducted for two sites- near border Front and far border TJ Estuary site. Quartz filters were analyzed to determine Organic Carbon (OC) and Elemental Carbon (EC) of PM2.5 using Thermal Optical Transmission (TOT) method, whereas, Teflon filters were examined for elemental (crustal and non- crustal) and ion analysis utilizing X-Ray Fluorescence and Ion Chromatography techniques, respectively. Seasonal variation was observed getting higher PM2.5 concentration during winter season as compared to summer season from all four sampling sites. OC was identified as the most abundant species within PM2.5. Summer represents higher fraction of OC/ PM2.5 in near border Front compare to coastal region TJ Estuary site (69% Vs 64%, respectively); whereas, winter season displays higher fraction of OC/ PM2.5 in far border TJ Estuary compared to near border Front site (72% Vs 58%, respectively). Significant positive correlations were observed among crustal elements (r= > 0.95) and also among metal elements (r= > 0.73). Source apportionment analysis using Chemical Mass Balance (CMB) model revealed that, combustion (mobile and industrial) was the major emission source, and biogenic, tire wear and secondary PM were the remaining prominent contributors of PM2.5 concentration in this region. Future air quality monitoring study should be continued to initiate proper mitigation plan so that better air quality can be ensured for the border community.