In　electron　tomography　(ET)　based　on　a　transmission　electron　microscope,　the　effective　thickness　of　a　specimen　increases　with　the　tilt　angle　and,　therefore,　the　projection　quality　may　deteriorate　because　of　electron　scattering.　The　information-missing　region,　however,　can　be　reduced　by　broadening　the　specimen　tilt　range.　To　clarify　the　general　influence　of　these　effects　on　ET,　the　projection　quality　varying　with　the　tilt　angle　was　quantitatively　evaluated　for　a　5-mum　thick　specimen　observed　with　a　3　MV　ultrahigh-voltage　electron　microscope.　Simulations　of　three-dimensional　reconstruction　were　then　performed　for　different　specimen　thicknesses　and　tilt　ranges.　As　a　result,　the　ET　accuracy　was　shown　to　decrease　as　the　specimen　thickness　increased.　However,　an　optimum　specimen-tilt　range,　at　which　ET　could　reach　its　highest　accuracy,　was　found　to　exist　and　become　small　with　the　increase　of　the　specimen　thickness.　The　presented　results　are　helpful　for　determining　the　specimen　thickness　limitation　on　the　ET　resolution　and　improving　the　ET　fidelity　of　thick　specimens.