Hola, Ayi! Basically, '성질' and '성격' have similar dictionary meanings. However, there are some differences between them in the usage. It can be said that '성질 ' has two meanings: the first is 'intrinsic properties or characteristics of things or phenomena' and the second is 'temper (in a negative sense)'. Although 성격' also means two meanings and its first meaning is similar to that of '성질', the second is quite different and means 'character, personality, and nature'. Let's focus on the second meaning of '성질' and '성격'. You can figure out these differences by checking the following examples: ✫성질✫ 1. 성질이 사나운: ill tempered; violent tempered 2. 급한 성질: short temper; impatient temper　 3. 못된 성질: bad temper; nasty temper 4. 성질을 부리다: lose [show] one's temper; explode in anger 5. 성질을 내다: go mad, have [throw] a tantrum 6. 성질을 죽이다: kill one's temper 2 and 3 can be replaced by '성격'. ✫성격✫ 1. 낙천적(인) 성격: optimistic personality [character] 2. 성격이 좋다: (≠ 성질이 좋다) to have a good character [personality] 3. 성격이 나쁘다: (≒ 성질이 나쁘다) to have a bad character [personality] 4. 느긋한 성격: (≠느긋한 성질) relaxed [easygoing] character 5. 신중한 성격: (≠신중한 성질) prudent character Although '성질' and '성격' are replaceable in some examples, it would be better not to use '성질' to older people in Korea as follows: 1) 아버지께서 성질이 급하시다. (This makes sense, but sounds rude and is inappropriate in honorifics. This should be corrected to '아버지께서 성격이 급하시다.') 2) 선생님은 욱하는 성질이 있으시다. (This also makes sense, but sounds rude and isn't proper in honorifics. This should be changed to '선생님께서는 화를 잘 내신다.')