Brutus' flaw is his naivete because he easily trusts Cassius and the other conspirators. He also thinks that the conspirators are killing Caesar for the same reason as him (which is for the good of Rome).
There are actually quite a few :
1) Idealism
2) Perfectionism
3) maybe naivety
4) poor judgment
5) his honour
6) thrust
7) gullibility
You are free to choose, each of the above can be supported though, so there is arguably not 1 tragic flaw.
Brutus actually believed that Romans in general would abandon Dictatorship in favour of an old-fashioned republic as long as Caesar wasn't there. However, dictatorship was emerging as the only effective way to rule to Roman Empire, and killing Caesar would not change that. Brutus was a political idealist.
Like most of the characteristics chosen as "tragic flaws", the characteristics of Brutus most usually chosen are in fact not flaws at all. Brutus was "an honourable man", "the most noble Roman of them all". These are good things. The message of the play is that an honourable man, a noble man, a man of incorruptible virtue, cannot succeed in a political world of corrupt realpolitik as practised by Mark Antony. It is not Brutus, but Rome which is flawed, and Brutus cannot cure that flaw simply by getting rid of Caesar. His tragedy is that he is flawless.
brutus is accusing cassius of having accepted bribes under his offfice
Marcus Brutus is in his 40's in Julius Caesar.
Brutus' trusted servant in Shakespeare's Julius Caesar.
Julius Caesar had an affair with Brutus' mother, Servilia. It is possible that Caesar was Brutus' father, but that is disputed by historians.
Brutus Cassius Portia Titinius Julius Caesar
Brutus is in Julius Caesar not Merchant of Venice.
Arrogance would certainly be a character flaw in Julius Caesar.
Marcus Brutus is in his 40's in Julius Caesar.
In the movie, Julius Caesar, Brutus was the last to stab him, but it is not certain who was the last to stab him.
Yes, with other conspirators: Julius CAESAR
Brutus' trusted servant in Shakespeare's Julius Caesar.
brutus
brutus
Brutus
Brutus was Julius' best friend.
Julius Caesar had an affair with Brutus' mother, Servilia. It is possible that Caesar was Brutus' father, but that is disputed by historians.
Brutus Cassius Portia Titinius Julius Caesar
Brutus is in Julius Caesar not Merchant of Venice.