There has been growing concern about the frying oil quality due to its remarkable deterioration during the frying process. To investigate the performance of LF-NMR in the rapid determination of frying oil from various frying conditions, deep frying oil samples (n=107) including 96 soy bean oil samples and 11 shortening samples were collected from street vendors in 10 districts of Shanghai. Total polar compounds (TPC) and viscosity of the oil samples were determined. TPC values of 6 oil samples (56% of all the oil samples) were above the national standard for frying oil, indicating the quality problem of frying oil from the street vendors. The linear analysis showed a good linear relationship (R2=0892) between TPC and viscosity, while R2 was 0927 after the removal of shortening samples. After the analysis of the ratio of T21 areas (S21) in transverse relaxation (T2) spectra, the good correlations between S21 and TPC and viscosity were obtained and R2 was 0860 and 0840. After removing the shortening samples, R2 slightly increased to 0865 and 0854. The results demonstrate that LF-NMR has the potential to rapidly evaluate the quality of deep frying oil.