Aimed at helping advisers decide which trusts to consider when building a client portfolio, the firm said it complements the current ratings for single strategy funds, SRI funds and multi asset fund ranges.
Geoff Mills, director of RSMR, said: "Investment trusts have not been as popular with advisers as open-ended funds for a variety of reasons. Availability on the larger fund platforms has been an issue and the big three platforms have been woefully slow in responding to the needs of advisers.
"In addition they have been seen as more complex and advisers are looking for a source of research in this area."

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The service has been created in response to rising demand from advisers since RDR, the firm said, with the AIC training over 3,000 advisers and purchases through platforms more than doubling.
Trusts will be measured by a range of criteria including gearing, liquidity and performance fees and qualitative evaluation of the fund management team and the investment process overall.
Mr Mills said: "We have seen increased demand for information and research so we felt we should help advisers and we have responded to these challenges by developing the new rating service to offer guidance and support to advisers and to help meet their requirements.
"Investment trusts can be viewed as a more difficult area to navigate and the RSMR seal of approval is an easy way to determine which investment trusts have passed our rigorous investment process.
"Initially there will be list of 15 but this will grow steadily as our research team analyse further companies and meet with managers as part of our research process."
A market insight guide has been developed to give further detail on the investment trust market and the key areas that advisers should be considering.
It can be used as structured CPD whilst also covering the full evaluation process that is applied by RSMR to each trust.
A separate list of rated trusts with supporting factsheets is available for advisers on a subscription basis.