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Second epoch of precise leveling observation network in Iran was performed for improving the leveling network quality in 2001-2009 interval. After correcting the ortometric, calibration, refraction and temperature extension effects on observation, pre adjustment tests were applied on the observation. Results indicate the quality improvement of the networks albeit the existence of the residual systematic errors. Standard error of precise leveling network is estimated to be ± 0.61 mm/√km after corrections. Least square adjustment was applied for estimation of leveling network heights by fixing the station near Shahid Rajayi port. The highest station of the network is the DDDH1110 in Jiroft road in Kerman province with 2887.856 m height. The least height of the network is AP-C1041 station in Mazandaran province with -25.678 m height. The least precision of the leveling network is 8 cm in DPDQ route maybe because DP and DQ loops are not closed. Analyzing adjustment results indicate the quadratic form of the closing error despite the non-normality of the residuals distribution because of remained systematic errors in observation.