Comparative studies on the morphometry of male genitalia and the frequency of clasper movements during induced copulation were done in the laboratory with colony strains of the natural mating Anopheles balabacensis (Perlis form) and the induced mating Anopheles dirus (Bangkok colony strain). In the Perlis form the width and the length of phallosome, coxite, style, and coxite plus style were significantly larger than in dirus on most particulars. The time of clasper movements, mating time and frequency of clasper movements in the Perlis form were also significantly less than in dirus. The results suggested that these two measurements can be used for differentiation of these two species. The mating behavior of stenogamy in the Perlis form and eurygamy in dirus were also discussed.