AbstractInterannual variations of photosynthesis in tropical seasonally dry vegetation are one of the dominant drivers to interannual variations of atmosphericCO2growth rate. Yet, the seasonal differences in the response of photosynthesis to climate variations in these ecosystems remain poorly understood. Here using Normalized Difference Vegetation Index (NDVI), we explored the response of photosynthesis of seasonally dry tropical vegetation to climatic variations in the dry and the wet seasons during the past three decades. We found significant (p < 0.01) differences between dry and wet seasons in the interannual response of photosynthesis to temperature (γint) and to precipitation (δint).γintis ~1% °C−1more negative andδintis ~8% 100 mm−1more positive in the dry season than in the wet season. Further analyses show that the seasonal difference inγintcan be explained by background moisture and temperature conditions. Positiveγintoccurred in wet season where mean temperature is lower than 27°C and precipitation is at least 60 mm larger than potential evapotranspiration. Two widely used Gross Primary Productivity (GPP) estimates (empirical modeling by machine‐learning algorithm applied to flux tower measurements, and nine process‐based carbon cycle models) were examined for theGPP–climate relationship over wet and dry seasons. TheGPPderived from empirical modeling can partly reproduce the divergence ofγint, while most process models cannot. The overestimate by process models on negative impacts by warmer temperature during the wet season highlights the shortcomings of current carbon cycle models in representing interactive impacts of temperature and moisture on photosynthesis. Improving representations on soil water uptake, leaf temperature, nitrogen cycling, and soil moisture may help improve modeling skills in reproducing seasonal differences of photosynthesis–climate relationship and thus the projection for impacts of climate change on tropical carbon cycle.