Under the new proposals, fund managers will be able to choose whether to adopt either a single or dual pricing mechanism for their units.
This should allow managers to select the method of pricing that best matches the information needs and expectations of investors in their funds.
The dual pricing system quotes two different prices to buyers and sellers of units.
Under the current rules, only authorized unit trusts (AUTs) are allowed to quote either single or dual prices, with investment companies with variable capital being forced to value under the single price system.
Dan Waters, FSA director retail policy and asset management sector leader, said that the new rules would put more responsibility on fund managers.
"No method of unit pricing is perfect or demonstrably superior to others in every situation," said Mr Waters.
"It fits with the principles-based regulation we seek to operate that each fund manager should judge for itself how to meet the needs and expectations of investors, provided the method adopted is compatible with fundamental standards of accuracy and transparency," he added.