Epitaxial ferroelectric thin films on single-crystal substrates generally show a preferred domain orientation in one direction over the other in demonstration of a poor polarization retention. This behavior will affect their application in nonvolatile ferroelectric random access memories where bipolar polarization states are used to store the logic 0 and 1 data. Here the retention characteristics of BiFeO_3 thin films with SrRuO_3 bottom electrodes on both GdScO_3(110) and SrTiO_3(100) substrates are studied and compared, and the results of piezoresponse force microscopy provide a long time retention property of the films on two substrates. It is found that bismuth ferrite thin films grown on GdScO_3 substrates show no preferred domain variants in comparison with the preferred downward polarization orientation toward bottom electrodes on SrTiO_3 substrates. The retention test from a positive-up domain to a negative-down domain using a signal generator and an oscilloscope coincidentally shows bistable polarization states on the GdScO_3 substrate over a measuring time of 500 s, unlike the preferred domain orientation on SrTiO_3, where more than 65% of upward domains disappear after 1 s. In addition, different sizes of domains have been written and read by using the scanning tip of piezoresponse force microscopy; where the polarization can stabilize over one month. This study paves one route to improve the polarization retention property through the optimization of the lattice-mismatched stresses between films and substrates. Epitaxial ferroelectric thin films on single-crystal substrates generally show a preferred domain orientation in one direction over the other in demonstration of a poor polarization retention. This behavior will affect their application in nonvolatile ferroelectric random access memories where bipolar polarization states are used to store the Logic 0 and 1 data. Here the retention characteristics of BiFeO_3 thin films with SrRuO_3 bottom electrodes on both GdScO_3 (110) and SrTiO_3 (100) substrates are studied and compared, and the results of piezoresponse force microscopy provide a long time retention property of the films on two substrates. It is found that bismuth ferrite thin films grown on GdScO 3 substrates show no preferred domain variants in comparison with the preferred downward polarization orientation toward bottom electrodes on SrTiO 3 substrates. The retention test from a positive-up domain to a negative- down domain using a signal generator and an oscilloscope coincidentally shows bistable polarization states on the GdScO_3 substrate over a measuring time of 500 s, unlike the preferred domain orientation on SrTiO_3, where more than 65% of upward domains disappear after 1 s. In addition, different sizes of domains have been written and read by using the scanning tip of piezoresponse force microscopy; where the polarization can stabilize more than one month. This study paves one route to improve the polarization retention property through the optimization of the lattice-mismatched stresses between films and substrates.