Repellent efficacies of two natural aroma compounds, citronella and citronellal, against mosquitoes, Culex pipiens pallens, were evaluated both in field and in vitro. In vitro, the experiment was conducted with three controlled bands impregnated with $30\%$ citronella extract, $15\%$ citronella extract and $30\%$ citronellal extract, and with bands impregnated $30\%$ citronella in field. Data was obtained by the means of counting numbers bitten by mosquitoes per unit time, namely human bait method. Percentage repellencies of above three controlled bands were calculated at $86\%,;73\%,;and;78\%$, respectively in vitro, and 80% in field, showing high repellent effectiveness against mosquitoes. This estimation was also confirmed by t-test compared between control group and each experimental group.