The interior is remarkable for its austere simplicity. The chancel is out of line with the nave, being deflected to S. From the nave the chancel is barely visible through the low crossing arch. Entry into stone-flagged porch with collar-rafter roof and stone bench (left). Porch C19 inner doorway has pointed arch with dripmould and foliated stops. The majestic nave with its high and narrow white-washed walls has a fine arch- braced collar-rafter roof. Nave is of 5 bays. The octagonal piers have moulded capitals and are set on octagonal moulded bases and have double-chamfered pointed arches. Above the depressed chamfered arch of the crossing , the upper wall (to right) has a pointed arched doorway to former gallery. From the angles of the tower crossing, four massive oak posts rise about 20m to support the bell chamber. The original five bells, inscribed with prayers for the church and for Queen Anne, and a sixth dated 1821, were recast in 1978- 9. Chancel walls are stripped. Fine arch-braced collar-rafter roof has battlemented wall-plate and cambered tie beams with painted decoration to soffits. C14 piscina with chamfered pointed arch, cinquefoil head and foliated finial. Set into the tower buttress of SW wall at ground-level, is blocked ogee-arched doorway. On adjoining S wall, blocked upper doorway with flat head has chamfered surround with pyramid stops. At ground level are two further blocked openings: to left, a segmental arched doorway with stone voussoirs and keystone, and to right a chamfered pointed-arched doorway with pyramid stops. The Cillwch chapel is separated from the chancel by an arcade of three depressed pointed arches. The arches nearest the tower have piers with attached shafts, one with a mask at impost level (‘the green man'), and complex ovolo and cavetto moulded arch. The arcade has two squints aligned towards chancel altar. Cillwch chapel has moulded late C17 altar rail with turned bulbous balusters. Either side of the E window of the chapel, are stone corbels with a king's head (said to represent King Edward II, and possibly early C14). Furnishings: porch has massive medieval parish chest, over 3m long, made from oak planks, lid in two halves with strap hinges, and nave has C19 benches with shaped ends and close boarded backs. Stained glassE window, by Howard Martin of Celtic Studios. N aisle, two C18 windows (taken from Llantilio Court) with arms of (1) Sir David Gam and (2) Sir William Herbert, Earl of Pembroke. Cillwch Chapel E window by CE Kempe. In chancel are several good wall monuments and floor slabs, including: W wall, to Jane Hughes of Treadam (died 1815) oval slate tablet, with closed alabaster urn garlanded with foliage, by Reeves of Bath. N wall, rectangular alabaster tablet to John Morris (died 1753) framed by fluted Corinthian pilasters and flanked by acanthus scrolled tapering wing brackets has broken pediment with inset painted achievement. Also to Mary Lewis (died 1760), oval tablet surmounted by obelisk against which is a carved achievement, and fine monument to Mrs Mary Ann Bosanquet (died 1820) by John Flaxman; square alabaster tablet depicts dying figure surrounded by relatives or friends, reeded architrave with paterae at angles and inscribed tablet below. Between choir stalls are two fine floor slabs depicting (1) To man with wife (probably Jane and John Walderne, died 1620) and three sons in contemporary costume (2) To Vicar Owen Rodger (died 1660) which bears three candles, and ten angel's faces. Cillwch chapel, N wall has classical style wall monument to Thomas Medlycott (died 1738) with rectangular marble tablet flanked by fluted Corinthian columns and, above cornice, a painted achievement flanked by shells. Also on S wall, small tablet to James Watkins (died 1721) in style of Brute brothers, has sacred monogram inscribed in pediment with ball finial and winged angel in apron. In S transept, tower upper wall has rectangular tablet to Matthew Morgan (died 1761) with winged angel at head, by P & T Brute.