The present invention relates to a pharmaceutical composition for treating, preventing or improving premature ejaculation, which is taken on demand prior to sexual activity, the composition comprising clomipramine hydrochloride in an amount of 14 to 16 mg, preferably about 15mg, as an active ingredient. More preferably, the composition of the present invention further comprises pregelatinized starch and sodium starch glycolate. The pharmaceutical composition of the present invention can provide rapid onset of efficacy, reduce a dissolution (absorption) deviation according to the patient's gastrointestinal pH conditions and minimize side effects.