In order to achieve higher yields, easier weed control, less consumption of nutrients and water, vegetable growers in the cultivation of various vegetable crops often apply black polyethylene (PE) film for mulching. Mulch type can have a significant impact on the quantitative and qualitative characteristics of crops, which are also affected by environmental factors, i.e. chemical and physical properties of the soil and weather conditions during the growing season. Therefore, it is necessary to conduct studies that include different types of mulches and vegetable crops, different growing seasons and agro-ecological conditions. In the summer growing period in 2014 at the location Hrestenica, close to Pazin, a research was carried out to determine the impact of polymer and organic mulches, compared with uncovered soil, on the yield components of summer squash grown in the open field. Three hybrid cultivars of summer squash were used: 'Opal' with white fruits, 'Sofia' with green fruits and 'Cigal' with dark green fruits. In the field trial, black PE-film, black-and-white PE-film and polypropylene (PP) agro-textile (60 g/m2) were included out of polymer mulches and straw out of organic mulches, while the uncovered soil constituted the control variant. Twofactorial field trial was carried out by the randomized block design method in three repetitions. Seedlings were planted at a distance of 100 cm between rows and 50 cm between plants in a row. In the period from the first to the last harvest (28 June to 14 August), 21 harvests were performed. During the harvest period, morphological characteristics of fruits (weight, length and diameter) were determined and market yield of fruits was established afterwards. On the straw mulch all cultivars had the lowest marketable yields. The combination of cultivar 'Cigal' and black-white PE-mulch has justified higher marketable yield then a combination of all cultivars and uncovered soil, respectively, achieved a 30% higher yield than the combination of 'Opal' × uncovered soil and for 18.5% of the combination of 'Sofia' × uncovered soil and 'Cigal' × uncovered soil.