1、serious的副词是seriously，表示“严重地；严肃地”。
serious的名词是seriousness，表示“严肃；认真”
2、serious的比较级在其前面加more；最高级在其前面加most。
My English teacher is more serious than my Chinese teacher .
Mr. Zhao is the most serious in our school .
3、短语：
take sth. /sb. seriously 认真对待.....
You should take the matter seriously .