The fungicidal activities against phytopathogenic fungi of two aminothiazole compounds of N-[4-(4-fluoro)phenyl-2-aminothiazol-5-yl]pyrimidin-2-yl-N-subst. phenylamine (V-1, V-2) have been determined and these two compounds were used as the leading compounds in this study as V-1 for N-[4-(4-fluoro)phenyl-2-aminothiazol-5-yl]pyrimidin-2-yl-N-(3-hydroxymethyl)phenylamine and V-2 for N-[4-(4-fluoro)phenyl-2-aminothiazol-5-yl]pyrimidin-2-yl-N-3-(1-hydroxyethyl)phenylamine. Further syntheses of these two compounds, V-1 and V-2, were conducted by reacting them with three functional groups, 2-(N-ethoxycarbonyl)piperidin-4-yl, 2-piperidin-4-yl, and 2-(N-methyl)-piperidin-4-yl-thiazole. From this scheme, 21 compounds were newly synthesized and their structures were confirmed by $^1H$-NMR-spectrum. The fungicidal activities of all the synthesized compounds against Phytophthora capsici were examined using the whole plant method. While the $EC_{50}$ value of the commercial fungicide dimethomorph was 4.26 mM, that of IX-3g on P. capsici was 1.03 mM. Among the 21 chemicals, IX-3g showed the most potential antifungal activity in vivo. Therefore, IX-3g may be considered as a potential candidate for the control of phytopathogenic diseases characterized by P. capsici infection, and further studies will be conducted on the mode of action IX-3g.