Plasmodium falciparum can cause severe illness and mortality, especially in pregnant women and young children. Asexual stage and gametocyte cause harmful manifestations to the patients and contribute to the spread of the disease, respectively. Moreover, most recent therapeutic drugs did not affect the gametocyte. The discovery of a new drug with dual actions on both stages could elucidate a cost-effective way to combat malaria. Within a human host, the parasite possesses many activities for its survival, such as invasion, haemoglobin degradation, and protein trafficking, many of which are related to aspartyl protease, revealing the potential for antimalarial drug targets. To demonstrate the effects of pepstatin A, a board-spectrum aspartyl protease inhibitor, the number of parasites with stage distribution and morphological changes were evaluated under the microscope. Pepstatin A at 100 μM inhibited the asexual stage and early-stage gametocyte development by 47% and 73%, respectively. They exhibited morphological defects, including chromatin condensation, vacuolization and haemozoin clumping in both asexual blood-stage and early-stage gametocyte. However, it could not influence the late-stage gametocyte development and gamete formation. Inconclusion, pepstatin A moderately affected both asexual blood-stage and early-stage gametocyte development. Morphological changes on treated parasites implied the effect of pepstatin A on haemoglobin degradation, suggesting its potential for reducing the severity of the disease and minimizing malaria transmission. However, further research and development are required to use aspartyl protease as a drug target, focusing on identifying and modifying the drug to be more sensitive and effective.