ABSTRACT We present fBLS – a novel fast-folding technique to search for transiting planets, based on the fast-folding algorithm (FFA), which is extensively used in pulsar astronomy. For a given light curve with N data points, fBLS simultaneously produces all the binned phase-folded light curves for an array of Np trial periods. For each folded light curve produced by fBLS, the algorithm generates the standard BLS periodogram and statistics. The number of performed arithmetic operations is $\mathcal {O}(N_p⋅ \log N_p)$, while regular BLS requires $\mathcal {O}(N_p⋅ N)$ operations. fBLS can be used to detect small rocky transiting planets, with periods shorter than one day, a period range for which the computation is extensive. We demonstrate the capabilities of the new algorithm by performing a preliminary fBLS search for planets with ultra-short periods in the Kepler main-sequence light curves. In addition, we developed a simplistic signal validation scheme for vetting the planet candidates. This two-stage preliminary search identified all-known ultra-short planet candidates and found three new ones.