This study aims to examine the extent to which the psychological and behavioural problems are common among the students in the grades eleven and twelve and their relationship with the variables. A number of students from Nizwa schools have contributed to this study. To achieve the study aim, a tool made up of 68 passages has been developed and ascertained validity and reliability as it has reached (0.918) of the reliability measurement. The study sample consisted of 411 male and female students from different schools in Nizwa in al-Dakheliya Governorate. The researcher has used various statistical methods to collect the study questionnaire such as arithmetic means, standard deviations as well as T-TEST. She has also relied on the one-way analysis of variance (one-way ANOVA) to study the family issues such as parents presence, mother's death, father death and divorce and their effects on the prevalence of psychological and behavioural problems. The study results showed that there are no big differences in the effects of the study axis on the problem prevalence. According to the collected study statistics, it is clear that the results are ranging between the medium level, low and very low level. Based on the reached results, they have indicated that anger was in the highest rank of the causes of the psychological and behavioural problem and statically it was in a medium level. The second one was the low focus and attention paid in the class and it was also in a medium level. Low self esteem was the third one and it was of a low level. Lying and isolation were the fourth and fifth ranks respectively and of a low effect degree. The sixth one was family problems and was of a low degree effect and, eventually, the seventh two were aggressiveness and rebellion with a very low effect degree. Under the lights of the previously mentioned results, the researcher recommends the necessity of increasing the awareness of how to deal with the difficulties that the students could face; especially in both grade eleven and twelve. Thus, they would be able to face the society, deal with any problem they might encounter in the real world and avoid any psychological problem.