Abstract: Effects of low night temperature were investigated on two local hot pepper varieties ('Beldi' and 'Baklouti') grown at day/night temperature of either low night temperature regime (25?C/10?C) or optimum night temperature regime (25?C/20?C). The negative effect of low night temperature on floral structure differentiation was registered on both varieties. The deleterious effect was more sensitive on bud stage than on flower buds stage. Abortion of these structures was less important in 'Beldi' than in 'Baklouti'. Floral structure abortion induced by low night temperature was negatively and significantly correlated with soluble acid invertase activity on 'Beldi' (r=-0.82), while on 'Baklouti', both sucrose synthase and insoluble acid invertase activities were correlated with floral abortion (r=-0.78). Under low night temperatures, sucrose synthase and soluble acid invertase activities were reduced to 50%, while the insoluble acid invertase activity was reduced by more than 90%. Enzymatic activities and flowers abortion correlation show a differential response between these two parameters and the developmental stages of flowers.