Cucumber growing in the unheated greenhouses allows earlier planting than in the open field, where there is a risk of lower temperatures than the minimum for growth, which can affect the plant. Studies have shown that the biostimulants increase of the asimilation surface with a positive effect on increasing the plants resistance to stress conditions. Therefore, a study was carried out to test the influence of biostimulants Bioplex and EcoBooster 2 on the morphological properties of cucumber (cv. Bosco and Tajfun) and cucumber yield, compared to untreated control. Thirteen harvests were done in the period from 30 May to 25 July. In each harvest, the number and weight of the marketable and the share of unmarketable fruits were determined. Also, the morphological characteristics (length, diameter and weight) of the marketable fruits during the harvest period were observed. During the cucumber vegetation in the unheated greenhouse, significant variations of air temperature and relative humidity and the composition of the nutrient solution were noted. When monitoring morphological characteristics of fruits, it was found that the tested cultivars differed significantly, while the positive effect of the applied biostimulants was absent. Tested cultivars differed significantly on the weight of marketable fruits (236 g Bosco and 215 g Tajfun) and achieved marketable yield (3775 g/plant Bosco and 3160 g/plant Tajfun). There was no significant difference between applied biostimulants and control regarding marketable fruits weight and yield. Significant differences were found between interactions between cultivars and biostimulants, but they were caused by significant differences among tested cultivars. The fruit weight ranged from 214 to 248 g, and the marketable yield varied from 2836 to 3915 g/plant. Based on the achieved results it could be recommended to repeat the research with some earlier planting in the greenhouse with the possibility of microclimatic conditions regulation and with the selection of a higher number of cultivars and biostimulants to achieve more accurate results.