Lateral buds of potted mandarin plants (Citrus reticulata Balnco cv 'Balady') were treated with four concentrations of colchicine (0.0, 0.1, 0.5 and 1.0%) for five consecutive days in order to investigate colchicine effectiveness in producing tetraploid plants of important mandarin cultivar in Egypt. These tetraploid plants can later be used as parents for producing seedless triploid plants through hybridization with diploid ones. Colchicine treatments decreased bud sprouting percentage and reduced shoot length. Furthermore, increasing colchicine concentration reduced the number of stomata per unit area compared to the control; however, stomatal length and width increased proportionally. Based on chromosome counting, the highest tetraploid percentage (42.2%) was obtained at 1.0% colchicine followed by the treatment of 0.5% (35.6%), whereas 0.1% concentration achieved the lowest tetraploid percentage (11.3%). The tetraploid shoots exhibited a broader leaf area and bigger floral buds expressed in length and width compared to the diploid mother plants. The results indicate that 1.0% colchicine is the most effective concentration for producing tetraploid plants.