Is the interest on money borrowed on margin in/for an RRSP considered tax deductible?
I believe your question is based on a false premise. First, no broker, that I know of, provides an RRSP account that is a margin account. RRSP accounts follow cash settlement rules.  If you don't have the cash available, you can't buy a stock.  You can't borrow money from your broker within your RRSP. If you want to borrow money to invest in your RRSP, you must borrow outside from another source, and make a contribution to your RRSP.  And, if you do this, the loan interest is not considered tax deductible. In order for investment loan interest to be tax deductible, you'd need to invest outside of a registered type of account, e.g. using a regular non-tax-sheltered account. Even then, what you can deduct may be limited. Refer to CRA - Line 221 - Carrying charges and interest expenses: You can claim the following carrying charges and interest [...] [...]   You cannot deduct on line 221 any of the following amounts: