There　have　been　few　studies　regarding　the　torsional　behavior　of　FRP-reinforced　concrete　members.　Only　the　CSA　S806-12　and　the　ACI　440.11-22　codes　specify　the　design　criteria　for　their　pure　torsional　capacities.　A　meso-scale　numerical　model　of　circular/square　concrete　columns　with　BFRP　bars　was　developed,　in　which　concrete　heterogeneity　can　be　explicitly　described.　This　study　evaluated　longitudinal　reinforcement　ratios,　stirrup　ratios,　cross-section　shape,　and　structural　size　for　their　effects　on　BFRP-reinforced　concrete　column　torsional　performance.　For　BFRP-reinforced　concrete　columns,　the　nominal　torsional　strength　exhibits　a　significant　size　effect,　while　the　longitudinal　reinforcement　and　stirrups　ratio　cannot　suppress　the　size　effect.　Furthermore,　a　modified　size　effect　law　was　developed　to　quantitatively　reflect　the　relationship　between　nominal　torsional　strength　and　structural　size.　BFRP-reinforced　concrete　columns　present　a　more　substantial　size　effect　than　steel-reinforced　ones.　Finally,　a　modified　calculation　formula　of　pure　torsional　capacity　was　proposed　considering　the　effect　of　structural　size.