Rates on the products start at 3.19 per cent and have a two per cent arrangement fee with loans of up to £1.5m available for individual and limited companies.
Previously the reciprocal 60 per cent loan to value (LTV) deal was at 3.39 per cent with a 1.5 per cent product fee.
Zephyr will lend up to £1.5m on its standard range at up to 70 per cent LTV and up to £1m with a 75 per cent LTV.
Managing director Paul Fryers said: “We are delighted to offer a reduced and highly competitive Spring Special on our five-year fixed rate product which coincides with the peak property buying season.
“The new rates are one of the lowest in the specialist buy-to-let market today, offering landlords and property investors further product options when considering either plans to purchase a new property or re-finance existing mortgages.”