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Continuous in situ measurements of aerosol optical properties have been conducted since March 2010 at a semi-arid rural site in Northeastern China - Tongyu (44.56 degrees N, 122.92 degrees N, elevation 151 m), a reference site of Coordinate Water and Energy cycle Observation Project (CEOP). Aerosol optical properties derived from the measurements during two spring seasons in 2010 and 2011 are analyzed and presented here. Mean values (and standard deviation) of light absorption coefficient (sigma(ab)) and scattering coefficient (sigma(sc)) at 520 nm were 7.61 Mm(-1) (6.17 Mm(-1)) and 89.22 Mm(-1) (88.37 Mm(-1)), respectively, in spring of 2010, and were 7.01 Mm(-1) (5.60 Mm(-1)) and 85.34 Mm(-1) (116.11 Mm(-1)), respectively, in spring 2011. These values are lower than the majority of measurements made in other areas of China. The mean single scattering albedo (omega) was 0.90, greater than values found in some developed areas in China, indicating more scattering or less absorbing aerosols at Tongyu site. Mean values (and standard deviation) of the Angstrom exponent of absorption (alpha(ab)) were 1.61 (0.27) and 1.64 (0.28) for spring of 2010 and 2011, respectively, and of the scattering (alpha(sc)) were 1.48 (0.50) and 1.10 (0.50), respectively. The values of alpha(ab) were higher than those of pure BC, implying the presence of other light absorbing materials having larger alpha(ab) values. The moderate values of alpha(sc) indicated that considerable amount of coarse particles presented at Tongyu site. Distinct diurnal variations of aerosol optical properties were observed. omega, alpha(ab) and alpha(sc) had nearly opposite diurnal variations compared to those of sigma(ab) and sigma(sc). Dust aerosols from the northwest and anthropogenic aerosols from the south were major sources contributing to the episodic aerosol events and thus, unusual aerosol optical properties, in spring at Tongyu site. High levels of PM2.5, if mainly caused by dust particles, do not necessarily introduce high values of sigma(ab) and sigma(sc).