Quantifying the sensitivity of ecosystems to droughts, particularly with different seasonal timing, could improve our predictions of ecosystem-climate feedbacks, but few experiments have explicitly addressed seasonal timing per se effects on ecosystem sensitivity to droughts. Here, we present a seasonal timing × drought manipulation experiment to examine sensitivity (relative change in response parameters to the relative change in precipitation) of key ecosystem processes (community biomass and ecosystem CO2 fluxes) to pulse-drought with different seasonal timing (early, middle or late) on a temperate semiarid grassland. We found belowground and total biomass were positively sensitive (i.e. ecological processes promoted by droughts and vice versa) to early and middle droughts but negatively sensitive to late drought while aboveground biomass was insensitive to all droughts. Ecosystem CO2 fluxes had the largest negative sensitivity to early drought and smallest negative sensitivity to middle drought, although gross ecosystem production showed larger negative response to droughts than ecosystem respiration, leading to reduction in net ecosystem production, regardless of seasonal timing. Our results highlight the crucial role of seasonal drought timing in regulating sensitivity of key carbon cycle processes to droughts and suggest that droughts at plant peak stage cause the least detrimental ecological consequences.