Vapour pressure deficit (VPD) inside protective structures under cropped conditions significantly affects the plant growth and productivity through its direct relationship with crop transpiration or irrigation management. Thus, monitoring VPD inside greenhouse during crop growth period becomes essential to limit it to a desired range. The present study was undertaken to develop mathematical models for predicting SVP, AVP and VPD inside a greenhouse independently using internal and external climatic parameters as inputs. The root mean square error (RMSE) was obtained in the range of 0.03-0.10 kPa and 0.27-1.03 kPa respectively for the models developed from internal and external climatic parameters as model inputs. The average model efficiency (neff) was computed to be 98.7 per cent, 92.2 per cent and 100.0 per cent respectively for SVP, AVP and VPD when predictions were made using internal climate as input. Similarly, for the models developed from external climate as model input, neff was worked out to be 96.7, 86.1 and 93.0 per cent for SVP, AVP and VPD respectively. The developed models presented a high degree of precision in predicting SVP, AVP and VPD with both internal and external climatic conditions as model inputs inside a naturally ventilated greenhouse under cucumber crop in soilless media.