Twenty-one mini watermelon [Citrullus lanatus (Thunb.) Matsumura & Nakai] hybrids and their 6 parents were grown at Experimental area of the Department of Horticulture, Faculty of Agriculture, University of Cukurova in Turkey with the aim of assessing heterosis in plant and fruit parameters as well as total fruit yield. Performance of hybrids was compared with their parents in stem length, stem diameter, number of nodes, flowering time, total yield, fruit weight, fruit height and diameter, rind thickness and total soluble solid content. According to the research results there was no significant difference in stem length and stem diameter; however, all other investigated traits were found significantly different among hybrids and parents. Percentage heterosis was assessed in all 9 traits and maximum positive heterosis (95.38%) was obtained in hybrid 29 x 1 for number of nodes followed by 82.58% in hybrid 21 x 29 for total fruit yield. The highest negative heterosis (-39.65%) was found in hybrid 29 x 1 for total fruit yield and followed by -37.04%, for fruit weight in hybrid 21 x 19.