A plant disease-controlling agent containing as an effective ingredient a pyrazoline derivative represented by the general formula ##STR1## wherein, R.sup.1 to R.sup.4 denote hydrogen atoms, etc., R.sup.5 denotes a hydrogen atom, etc., R.sup.6 and R.sup.7 are the same or different and denote optionally substituted hydrocarbon groups, and R.sup.8 and R.sup.9 are the same or different and denote hydrogen atoms, etc., provided that not all of R.sup.1 to R.sup.5 denote hydrogen atoms at the same time. The pyrazoline derivatives represented by the above general formula exhibit excellent control effects on plant diseases.