The present study investigates the reasons behind the misuse of English prepositions “in” and “on”. This study tried to find out if the misuse of the English prepositions is related to the interlanguage errors (the interference of mother tongue) or related to intralingual errors (due to the English language structure itself) or there are other factors which cause the misuse of English prepositions for the university students. The data is sampled from a (Test) distributed to students almost around (40) at King Khalid University, College of Science & Arts in Ahad