Abstract: Radiation efficiencies of QSOs are believed to be determined by the angular momenta of their central Massive Black Holes (MBH). Assembly histories of MBH may have shaped their angular momenta. In this paper we estimate radiation efficiencies of selected low-redshift SDSS QSOs (0.025<z<0.5). Using estimated Virial-mass values to approximate the MBH mass (M_.) values, we fit predictions of the standard model of thin accretion disks to observed optical luminosities of the QSOs to individually estimate their accretion rates. The bolometric luminosity of each QSO is estimated by extrapolating its observed optical luminosities in different bandpasses using empirical panchromatic templates established through various observations. With the estimated accretion rate and bolometric luminosity we obtain the radiation efficiency of each QSO. We find a strong correlation between the radiation efficiency (ε) and the black-hole mass, ε∝M_.^0.63, which is similar to the result of Davis & Laor (2011). The estimated radiation efficiency of an individual MBH has a large error which includes errors propagated from various sources. We further discuss various possible biases involved in the estimates of the radiation efficiencies, as these biases potentially contribute to the result ε-M_. relation. These include the uncertainty of approximating the MBH mass with the estimated Virial mass, the oversimplification of the accretion-disk model, the sample selection effects, and the errors of the estimated bolometric luminosities due to the limited database for templates and unknown dust/gas obscuration.n